Insulating a Log Cabin Floor and Roof

If you were one of my customers and you were buying a lovely new log cabin from me, especially one of our thicker wall log cabins such as 50mm upwards, I would be strongly urging you to insulate at the least the floor of your new log cabin. I would also try to nudge you to insulate the roof as well.

You may also be interested in this post on double glazing, R and U values and Log cabin thermal properties: Double Glazing in Log Cabins

The benefits are obvious for you.  You’ve decided upon your building, you’ve weighed up the benefits of the thicker logs and of course the double glazing.  But, a lot of heat is lost from the floor and it’s cold rising up and of course loads is lost through the roof.  Ideally we want these areas insulated and to the same or similar as the wall thickness.

Lots of retailers supply ‘insulation kits’ with their buildings, we don’t, but we could, we could make a bit of money out of it as well.  But seeing as the cabins are costly enough as it is do you really want to add more cost if you can help it.  So, instead of me supplying you a special insulation package and making some money from it I’ll tell you how to do it yourself and save money or better still spend the saving on better quality insulation.  All the insulation I talk about is ordered through any builders merchant, most of which will deliver to you at the fraction of the cost of a retailers special ‘Insulation pack’.

I like the Celotex brand of board, I’ve used several types over the years but get on best with this one.


Here’s a link where you can download more details on the product:  Product Details

I know lots of other manufacturers do a similar product, some better and some worse, that part is up to you but I prefer a solid fibre board to work with as above.

Of course there are lots of ways to accomplish an insulated roof and floor.  Some fitters favour adding it underneath the roof and boarding it out thus keeping the insulation in.  Some will put a frame on top of the roof and use rockwool and ply over the top.  I have never used these methods as I can’t see the benefit other than perhaps a saving in the insulation material cost itself.

So, my rough and simple guide on how to insulate your roof and floor of your new log cabin.

Insulate the floor

A quick one before explaining this:  Have you considered a DPM?  A damp proof membrane either within your base or on top of it.  It’s well worth it and prevents any damp coming up and into your building. (

I build my log cabin as usual on the 44mm tanalised timber foundation beams we supply with every building and I’ve now completed the build.  I’m left with the floor to put down and the roof covering to apply.  If I’m using a floor pack I will set out my floor bearers as normal.  I then cut up my insulation board which I’ve ordered from the local builders merchant at 50mm deep.  This sits perfectly between and within the bearers, the joists support my build while the insulation boards supports it. If you want to be exact to the joists then use 40mm.

Insulation board is placed within the bearers

Insulation board is placed within the bearers

Now I simply lay my floor boards as normal, happy that the floor is insulated.

Another method is to not bother with the floor pack and to fill the inner area of the cabin with the insulation boards.  On top of that you use far cheaper OSB sheets or chipboard flooring, this is especially relevant if you are later putting down carpet as OSB is certainly cheaper than our nice T&G pine.

Obviously you’ll need to work out how much board you need with a simple calculation of length x breadth to find the square meter and order the equivalent from your local builders merchant.

Insulating the Roof of your log cabin:

The roof is a little trickier to do and takes a little more work.  Before we start you need to decide what thickness of insulation board to use.  50mm, the same as the floor is very convenient and often used.  You could also go up to 70mm to gain the same R value.  I have also used 100mm when specified by planners.  Regardless the same principle applies.

Work out how much you need by calculating one side of the roof area and times it by two.  As well as the insulation boards you will also need to order longer clout nails.  These need to be long enough to go through the final roof surface, insulation and into the roof timber boards.  If you’re using 50mm insulation then order 65mm nails for the flats of the roof and 70mm clout nails for the ridges.

Lay the boards so they are flush with the leading edge.  Bare in mind this is going to be exposed so consider how you’re going to cover it.  In this example we were using 50mm board and turned the roof trim the other way up:

Roof trim along the leading edge ready for the insulation board

Roof trim along the leading edge ready for the insulation board

You can also cover this portion later with additional timber but it is worth considering it at this point.  You may need to source locally the additional trim timber.

Now lay one layer of insulation boards and fix into place using one clout nail in each corner and one in the center.  You can then felt or shingle it up to that first board.  Don’t be tempted to do the whole roof with the insulation as you will eventually have to get on the roof to tile or felt it and with the whole roof done it can be very slippery.

Once a board is complete with tiles or felt move on to the next and carry on adding boards and tiles until you reach the top.

Insulating a log cabin roof

Insulating a log cabin roof

For tips on shingling your roof please see this post: Tips on how to fit Felt Shingles on your Log cabin


The last consideration is the bargeboards to the front and back.  You can either move the supplied one up or double up the barge boards as below, again you may need to source this additional timber locally:


The same principle also applied to hipped, octagonal and hexagonal roof.  The only slight difference is that  you will finish the corners of the ridges slightly differently where by you will cut them flush with the end of the roof boards.  You will then cut a fillet to fill in the ‘v’ that naturally forms.

One last tip, if you haven’t got a timber saw or a proper board saw, your wives bread knife works a treat for cutting the insulation boards!

Insulated Log Cabin

Insulated Log Cabin

More on insulating a log cabin can be seen here, it’s a bit of a rant about the current trends in the ‘Log cabin industry’ and all the rip off’s that abound. Please see here: More on Log Cabin Insulation

You may also be interested in this post on double glazing, R and U values and Log cabin thermal properties: Double Glazing in Log Cabins

Please see the following article of how to make insulated walls, partition walls and how to use thicker insulation in the roof: Dealing with expansion and contraction in Log Cabins

Finishing the Leading Edge.

Recently I have been asked for more details on how to finish the leading edge of the roof, hopefully this sketch will give you some ideas:

Ideas for finishing the leading edge of the roof.

106 thoughts on “Insulating a Log Cabin Floor and Roof

  1. I am contemplating buying a log cabin to use it as an extra bedroom. I therefore would like to insulate the floor, roof and wall. You have mentioned a few times about floor and roof insulation but rarely wall insulation.
    What is you thought on insulating the wall on the inside with a 50mm celotex, vapour barrier and plyboard (as wall finish)?

    • It’s not usually necessary to insulate the walls if a thick enough log is chosen. If you do insulate the walls you need to consider the natural expansion and contraction of the logs and make allowance for it in your design. Please see this article which will give you information on this: Expansion in Log Cabins

  2. Thanks for this guide. Can I please ask about vapour control layers and/or breathable membranes, since I am confused by different advice on these. We are aiming to insulate our cabin roof (a 16 degree pitched roof) using Celotex or similar PIR boards on the outside of the roof (on top of the wooden roof boards) before the waterproof layer. I understand we will have a “warm roof”. Do we need either a vapour control barrier or breathable membrane as part of this system anywhere? I notice you don’t mention these in your article. We are also planning to use an EPDM sheet for waterproofing (even though I note that you don’t think these look very nice on pitched roofs!) I am guessing we will need to cover the PIR boards with a layer of ply so that there is something for the EPDM to be stuck to?

    Many thanks.

    • I don’t usually use a membrane as with just 50mm of insulation and then felt on top there is not a need to in my opinion. If you are sandwiching the insulation such as adding a plywood top to stick EPDM onto it is a good idea to introduce an airflow above the insulation and below the upper board.

      • Thank you, Richard, for your prompt reply.

        We are wondering about using Plylok, which is PIR insulation with a 6mm layer of ply on top. It may work out cheaper than buying separate layers of PIR then ply, especially when you factor in labour time. With the Plylok the ply is pre-bonded to the PIR, and we’d glue the EPDM membrane on top of this. So, we’d be unable to create an airflow as you suggest above. In that situation should we use a vapour membrane on the roof boards, before laying the Plylok. (And wouldn’t fixing down the Plylok make holes in the vapour membrane?

        Costs are starting to mount up, and we are now wondering about reverting to a ‘cold roof’ system, with PIR between the rafters on the inside of the roof, with an air gap between the PIR and the roof boards. Would this suffice?

        Many thanks for your time.

        • I haven’t used this product before but looking at their instructions they are recommending a vapour control layer on top of the roof before the insulation is applied.

          I would not put the insulation inside if at all possible. With it inside you can create horrible problems with condensation build up.

          • Thank you, Richard. Very helpful as always. If we went ahead with insulation on the outside, and used a vapour control layer on top of the roof, can we still nail/screw through it to fix the PIR boards to the roof boards without completely ruining its function? Many thanks.

      • Hi Richard, SO have purchased a Meaghan cabin and have it built ready to insulate the roof and floor, I went for the profiled foundation beam which I’m now slightly regretting as it means the cabin sits that much lower to the ground and therefore theres only 45mm to the top of the door step, leaving only enough room for 25mm insulation….hopefully the somethings better than nothing rule applies. My worry is the roof; looking at your ideas above you say that putting the singles directly ontop of the celotex will be fine…wont the celotex end up being damaged with no wood to protect it, especially if im kneeling on it to work up the roof as you describe?
        Great info, really helped the build, thank you!

        • I wouldn’t regret the composite beams, they last forever, they look far better and they help with drainage. If you wish for a larger cavity between the base and floor boards to accommodate insulation you will put the floor joists first around the perimeter so you are not relying on the lip of the foundation beams. You can also raise the door frame slightly higher with a shim under it so becomes level with the top of the floorboard. You could also simply chamfer any step.

          Some damage will occur to the roof insulation as you are nailing through it. I haven’t experienced damage on the roof as long as you spread your weight, you could also use a crawling board. Certainly though a knee as the single point of contact will dent the insulation board. You can of course frame and cover the insulation with a board with the shingles on top but this is extra work, extra weight and expense that in my opinion is not really needed.

        • Hiya Just seen your query with regards insulation for the floor, we were in a similar position with our Karen Cabin the difference being is that they had changed the design thickness of the door threshold to what we were told when planning the base so we did not have enough height to put flooring such as laminate or carpet down.
          So we had to shim up the door frame, it works OK just bare in mind that you have to notch the first log on top of the door frame the same as the thickness as the shim you use to allow for expansion.

          With regards insulation on top of the roof.
          We not going to bother insulating the roof but we concerned about the thickness of the T&G roof boards supplied when they arrived as they do not look that substantial , maybe they are OK for a load such as snow but as our cabin is near a tree and we were concerned about the impact of falling branches damaging the roof boards.
          So as a last minute thing we decided to use insulation boards to spread the impact load of any large falling branches.
          I used thick 30 mm insulation from Quin Them and used the timber Tuin supplied which were 25×30 on top of the roof to attach the side barge boards to and act as a retaining frame for the insulation, this also meant that we did not have to mess around with the Apex barge boards as they looked OK when we fitted them.

          Anyway I crawled sideways all over the insulation with the odd time on my knees with hardly any indentions or damage to the insulation (I am 12stone or 90Kg).

          Also we did as another poster suggested by cutting the insulation edge at an angle so that there is not a V at the apex of the ridge this worked well.

          You may of thought about it all ready but I ran the cables for roof lights along the roof before I put the insulation on, checked with my electrician for the size of cable and that he was OK with it run below insulation and because its protected by an RCD he said it was OK.

          Hope that helps.

  3. Hi Richard,

    Your advice is absolutely brilliant. These blogs are invaluable.

    As the soon to be owner of your glorious Gijs cabin I have a quick one for you. I plan to follow your advice and install Koolspan 50mm insulation to the roof boards (on the outside). Brilliant and simple. However, As the Gijs has a 2m verandah I think it is overkill to insulate the overhanging part of the roof. Also expensive as insulation is quite pricey. So, I was wondering, how have you tackled this on your Gijs installs? How do you insulate part of a roof?

    I guess the simple things is to do the whole roof, but I am loath to waste money. Any thoughts would be very helpful.

    Very best


    • I understand the cost but it really in the simplest way to do it and insulate the whole roof. If you did want to save money you could add a frame and a board to bring the canopy up to the same level. It would be quite a bit of faffing but could be done.

  4. Our Chloe cabin sits on a timber frame, raised off an old, uneven concrete pad, using adjustable joist supports. The gap between the support frame and the floor joists and the concrete pad varies from 5mm to about 40mm across the whole area. Do you think it is worth laying some dpm under the floor joists before I insulate and board it out? I thought it might be better not too, to maintain a little airflow? Thanks

  5. Hi My log cabin arrives next month. I plan on insulting the roof would I be doing the right thing by using 70mm insulation sandwiched between the roof boards and 9 mm OSB board on top ? Would I need use a breathable membrane ?

    • For a normal log cabin 50mm should be enough done the way I have suggested. For the bigger cabins, 70, 90mm thick logs then yes 70mm sandwiched is a good idea. I wouldn’t do it on the thinner logs though as you are increasing the roof loading a lot. A breathable membrane is a good idea on larger building insulated differently.

      • Hi Richard So if I use 6 mm ply to keep weight down instead of the OSB would I still need to use a membrane or not and would I have to frame the roof to hold the insulation in place ?

        • You would need to frame the roof and cell it regardless. Consider as well the depth of wood you have to the felt nails assuming you are putting shingles on. If you are double layering it, it might be an idea to use a membrane. I only recommend this for the larger 70mm plus buildings.

  6. I have a question regarding the need for a DPM. I know this has probably been answered before on the blog but I’m seeing some conflicting information. I have built my cabin on timber bearers sitting on concrete blocks. So far I haven’t been able to incorporate a DPM and I can’t quite work out where it would go at this stage. Without it the joists will be sitting around 6 inches above the bare earth. Is it neccessary to use a DPM in this situation? Will the airflow take care of any damp rising? The only place I can think to put it is on top of the joists and lay the floorboards on top, but that would mean nailing through the DPM. Is this advisable or would I be better just leaving it out altogether? Any advice would be very much appreciated. Thanks.

    • Ideally I would still use a DPM even with the air flow, you can then be sure you’ve done your best to stop damp coming up from the floor. You could place it either under or on top of your floor joists. Under would be ideal.

  7. Hi
    Some help please.. Why the need for the 70mm clout nails for the ridge? Just about to put 50mm insulation and shingles on the TRUUS and have 65mm clouts, and wondering what is the best way to do the ridge as there will be a V Gap where the 2 x insulation board end, do we fill that with cut insulation in shape of a V? Any ideas welcome. Thanks. – thanks for help.

    • I like to use longer nails on the ridge as there is more felt to go through, plus the ridge is exposed and I like to make sure everything stays put. There will be a V where the two boards meet, I have never really worried about this as it is directly on top of a purlin and the insulation properties remain the same. If you wish you could infill it with off cuts.

  8. Hi Richard

    I have just fitted all the roof planks on my 45 mm Clockhouse and intend insulating with 50 mm Celotex. However I am a bit apprehensive at the slope of the roof at 35 degrees. You recommend in your article that I insulate a board at a time and fit the shingles as normal using 65 mm clout nails. However at some point I have to climb on to the roof with my feet and knees providing the necessary friction to keep me in place. Terrifying to say the least. I am concerned about my safety first and damage to the Celotex and shingles second. With only three clout nails holding the shingles surely they will tear trying to hold me in place!!!!

    What method/technique would you use or suggest to keep me safe and prevent and damage?

    • With tall buildings or ones that have a very steep roof pitch it is best to consider the use of scaffolding / scaffold tower and / or a safety harness and line secured to the opposite side of the building you are working on.

      I will also use a spare log or a deal screwed to the roof, on top of the shingles I have previously laid to act as as a foot hold. As I move up the roof the log is repositioned. On very large buildings I have used more than one.

      Any hole in the shingles can be filled with silicone and grit from surrounding shingles then sprinkled on top of the silicon so it is not seen and remains water tight.

      • Hi Richard

        Thanks for your reply.

        Your spare log idea inspired me. I have screwed a length of 2 X 1 ( I am an inches man) to the edge of the roof planking to which I have screwed a length of decking with the other end cut at an angle to secure it tight against the clock tower. As I moved up the roof I added another piece of decking to form the next step. Worked perfectly. I used a left over piece of planking to put under my knees to prevent damage to the shingles and the Celotex.

        To begin with and to gain confidence I used a length of rope round my waist and secured to a wheel barrow full of rubble on the other side of the clockhouse.

        Many thanks

    • Hi Douglas, I’m sure Richard will reply but i have literally just gone through this process so thought I’d chip in.

      The reason to put the insulation and shingles on one insulation sheet at a time is so that you can be on the wooden roof boards while you’re doing it. Not that you shouldn’t still be very careful, but I felt secure and stable sitting in the wooden boards, for hours on end.

      I started in this ideal fashion, going sheet by sheet, however due to weather concerns I finished the first day of this by putting all of the insulation up at once, using a few clout nails to hold it in place without the shingles. This worked well, but made things much much more difficult. The celotex is slippy! Although let me reassure you on one point… It will take your weight. I’ve been scrambling around on it all week and it’s fine. Be careful with knees and elbows, and I ended up taking my shoes and socks off in case the hard soles tore into it, but otherwise it’s surprisingly tough. Incidentally going barefoot also helped with friction on the celotex.

      • Hi Sam

        Thanks for your post. See my reply to Richard as to how I overcame my apprehension.

        You are correct in that the shingles and Celotex can take a lot of punishment. Before your post I was wary of putting any weight on them.

        Thanks again

  9. Hello, im thinking about buying one of these log cabins… you ever get. asked if you could supply someone to build them. im not sure I would manage to do it x

    • Tuin offers an insulation service as a company, we can also make recommendations of self employed installers who can be cheaper than our services as we have to account for VAT and working hours.

  10. I’m building my Uddel cabin at the weekend. Just checking, if i’m using 50mm celotex, i put the insulation on top of the roof, then the roofing felt directly on top with longer clout nails to fix? No OSB board needed between insulation and roof?
    Thanks in advance. Great site by the way, with loads of excellent advice.

    • Ideally with a flat roof it is best to use a sheet between the insulation and the final roof covering. With shingles it is not necessary as they are so thick but a roofing felt or EPDM is not really thick enough and you will have indents where the sheets of insulation meet.

  11. I’ve a quick question on insulating a floor, or rather a clarification:

    This article seems to suggest that if you’re not using floor boards but rather osb then it’s ok simply to not use joists and put the celotex directly on the damp proof membrane and the osb flooring directly on top of the celotex. Is this correct?

    Thanks for your time

    • Yes, in my experience you can put the OSB on top but bear in mind you will need joists to at least join the sheets. You will also need a perimeter fix as we do not want the floor to touch the log walls when it expands. Also, consider any heavy weight such as a pool table, gym stack etc, you will require joists to transfer heavy loads in these areas.

      • Thanks, Richard. I just wanted to check the details of your reply as I may be misinterpreting it (and please don’t hesitate to call me out on that!).

        Why do the sheets need joining with joists? Can they not be joined together just as they would be for the roof? Sheet-to-sheet?

        And regarding the “perimeter fix”, by this do you mean having a perimeter of joists a set few millimetres in from the wall to which the osb should be fixed?

          • You are correct, I am referring to the sheets, it would be ideal to be able to fix the sheets where they are joined. The sheet should not be touching the log cabin walls.

  12. Hi Richard, I’ve just taken delivery of a Ben Clockhouse with a 3.5m pitched roof. I was thinking of insulating but as it has 27mm t&g roofing, will I actually be gaining anything from insulating. We do plan to use the cabin all year round with a log burner. we will also have a hydrotherapy tub in there but don’t plan to use any other form of heating. Your opinion would be welcome.

    • The Ben Clockhouse Log Cabin is actually designed for the Irish market and is suitable for applying clay tiles hence the extra strength roof.

      I would still recommend you insulate the roof, the extra thick boards helps but insulation would be far better. I would like to see insulation both in the floor and the roof. This will make an extremely good all year around building and would not take too much to heat it.

      As you have a hydrotherapy tub I would also consider the treatment inside as you will get a build up of damp, I would also advise to fit a couple of vents in the log cabin due to possible moisture inside the building.

  13. Thinking of fitting 50mm celotex, monarfol 300 pitched roof underlay, roof shingles, what would be the best order to do this? Monarfol, Celotex, then shingles? Also would 65mm clout nails hold all this together ok ? Many thanks in advance .

    • I have never used an underlay when insulating a roof of a log cabin, I know some customers like to, I haven’t had any problem reported either way. 65mm nails and 70mm for the ridge works well with 50mm insulation and the shingles. I did a quick search and the membrane you are using is 0.3mm so it shouldn’t make much difference, again though I have no experience of this so please let us know how you get on. Customers have sent in pictures of the membrane going on first, then the insulation, then the shingles.

      • Hi RIchard, thanks for your reply, It’s a spare roll of Monarfol a neighbour gave me after roofing his brick garage so thought I would add it into the roof, also I have a deck that I built a few weeks ago out of 6inch x4inch 4800mm board to sit the cabin on and was wondering as regards to a dpm, I have a dpc for under the profiled foundation beams but wasn’t sure wether to fit a 4×3 dpm under my floor insulation to keep any stray water out that may get in from the egde of the profiled beams, would I be better leaving this out so the wood could breath although the wood would get air from underneath or fitting it to protect the insulation from any stray water ingress? Again many thanks.

        • Thank you for the picture of your base:

          ” alt=”Customer timber base” />

          As you have made a timber base the foundation beams are not always necessary if it is to the exact footprint. The profiled composite ones do look nice though if you have those and provide a lip over the base which provides a drip and nice profile. If the base is to the footprint you shouldn’t get any water coming through so a DPM is not really necessary. But, it looks as if you base is enclosed, if there is a DPM within it it should not be a problem, if not I would consider adding vents within it to allow for an airflow in the base itself.

  14. Hi guys
    I have a Karen on order with 40mm walls my question is can I fit 25mm insulated plasterboards to the internal walls…. Will I have to leave contraction slots on the lower fixing points and a gap at the bottom of the plasterboards for downward movement ??

  15. Believe insulating under the roof is referred to as cold deck construction. For the void I’ve seen a figure of 50mm but also seen a solution using rock wool (breathable insulation) over rigid foam (polystyrene) over vapour barrier and finally over roof cladding. Think on this blog I’ve also seen someone installing air vent grills into the void. Also seen a YouTube video that showed a simpler installation using multi layered foil insulation blanket tacked under roof boards and then clad. Looked really easy actually though understand the blanket may not be the cheapest material.

    Currently stuck on my project so doing more research on this topic then I really should.

  16. Hi Richard,
    In the information you give regarding roof and floor insulation, you mention that some people insulate the roof from the inside of their cabins. Although you say that your preferred method is on top of the roof you don’t actually dismiss doing it this way. Leading us to think that it can be done internally. However in the part entitled insulating the roof you then say it causes condensation doing it this way. A contradiction of paragraph one.
    Can you please advise us as unfortunately we didn’t realise that there could be a problem insulating from underneath the roof. Sadly we have already felted the roof in readiness for the Shirley to be added. Help please!
    Kind regards
    Jim & Ann Smith

    • I always prefer to insulate on top of the roof, this takes all the problems associated with condensation out of the roof. Of course I maybe wrong but it has worked well over the years for me.

      You can though insulate inside if you wish to. But, like any building including your house, allowances have to made for the moisture we expel living in it, the appliances we have and the moisture coming from the surrounding atmosphere and of course the ground / base.

      Linked above in this artice is another article where I give advice on insulating within a building: Dealing with Contraction and Expansion of Log Cabins

      The examples given should help to answer your question and avoid a contradiction, if any is found. The main point being to make sure you create a void and to ventilate that void well to allow any moisture to escape.

      Additionally insulating on top of the roof saves you unnecessary expense, a great deal of work, additional cladding or fascia and allows full height of the cabin internally. On occasions this is not always possible due to height restrictions. If you are forced to you can insulate under the roof but please make sure the void is vented otherwise, eventually the insulation wall fall down with moisture / water build up.

      We don’t really find felt necessary under shingles I do not recommend this personally, if the shingles are fitted correctly and as advised. The felt is only there to protect your building should the shingles blow off (apex roofs). If of course they are fitted as I advise they will not come off. My own, personal recommendation would be to leave the felt as is. Apply the insulation and then the shingles. You may need longer clout nails for this. Alternatively remove the felt completely. If you wish as some people do you can add a breathable membrane between the T&G roof and the insulation although I have not found this necessary either. Then you can add the final shingles. Alternatively, insulate from underneath leaving a void and a vent. What this void depth maybe I cannot advise as I have not done this.

  17. Hi Richard,

    To avoid nail so many holes through insulation board when we put nail through shingles and insulation board to the roof board, will it be better put a OSB board on top of insulation board,fix them to the original roof board, then nail the shingles to the OSB boards? I mean for 50mm insulation board. Do you think will it be ok? Also is it ok to put one layer underlay felt under shingles to make extra protection?

    Many thanks


  18. Hi Richard, I’ve just received the composite foundation beams and they sit 10mm proud all around my 100mm concrete base with 20mm gravel outside of this. I want to put in an insulated floor with celotex as you’ve suggested. Do I just put in some floor bearers inside, on the slab floor as the log cabin will sit on the profiled composite foundation beams and then add in the celotex inbetween before using the T&G flooring on top? The tanalised floor bearers will therefore sit on the concrete and would that allow damp to rise into the floor or sides of the cabin? Should I be sealing the profiled foundation beams all around the perimeter to stop any water flow? Thanks. Mark

    • Once the cabin is built on the foundation beams if you are using them then the floor ban be put in. If you choose to use floor joists these can be laid with the insulation in between them.

      It is important though to make sure you have a damp proof membrane in the base or at least on top of it. Please see the information I offer on log cabin bases for examples.

      If your base is not 100% level and you have gaps between the base and foundation then you will need to seal this.

      • Hi Richard, I have just order a Laula cabin without your floor. I would like some advice as to what size joist to put in, at what centers, I would like to insulate the floor ,and also should it be ventilated and how. Mike

        • Ideally joists will be around 45mm – 50mm in height, this gives you enough room for insulation and sits nicely at the door. Normally I would set these 300 – 350mm apart with an uninsulated floor. If I’m aware of extra weight points such as a set of weight stacks, piano or anything really heavy I will put the joists closer together in that area or provide a direct support.

          If you use a board like celotex and have joists slightly below or dead on you can have the joists further apart as the celotex, when supported on a concrete / slab / flat base, can take quite a bit of weight, I would then be considering 400 – 450mm as long as they are slightly below on the insulation depth.

  19. Hi Richard; Lots of great info as usual!

    Just took delivery of a Flow Cabin, and was wondering about the following:
    a) Using loft style insulation under the (floating) floor?

    b) Using same insulation, inside the cabin roof plus plasterboard and therefore any condensation issues?

    All much cheaper and similar R values to kingspan/Celotex etc.

    c)If I were to use 50mm Celotex on top of the roof, can I fix EDPM directly to it?

    Many thanks

    Tim Brigg

    • I’m pleased to hear the flow log cabin arrived safely for you.

      I cannot see any reason why fiberglass insulation cannot be used in the floor. I do prefer something like Celotex though as it’s easier to use and handle and does not compress.

      I would not recommend at all insulating the roof inside. Condensation can be a big issue, you will need to make sure it is well vented and I cannot give advice on what and how much. If the insulation is on top of the roof you do not ever have to worry about it.

      The flow is a flat roof log cabin. It is best to cell the roof with framing and then insulate with whatever material you choose and then put an OSB or similar board on top, then apply the final roof covering.

      EPDM or ERM will not be able to fixed directly on top of any insulation. Only felt tiles can do this with at least three clot nails used.

      EPDM or ERM is glued onto the surface and I would not recommend it being glued directly to the insulation.

      • Thanks Richard.
        One last question, hopefully;
        As we have a raised wooden base, supported on brick columns, is there any need to fix a DPM to the underside of it?
        If I do use loft insulation in the floor, I would as it would support the insulation, but celotex would be self supporting as it can fit in snug between the joists.
        Thanks again,
        Tim 🙂

        • I think you may as well fix a DPM, damp is still rising from the ground and it would not hurt to do it. If you use celotex you can fix battens either side of the joist to support the panel.

      • Hi Richard,

        Thanks for the help once again.
        Cabin up, mostly straightforward (purlins are hard work though!).
        Anyway, re your suggestion to construct roof with boards first, then kingspan and 11mm OSB covered in EPDM:
        Do you see any problem using the same order of things, except fixing the OSB directly to the top of the cabin, then working in reverse with kingspan next and have the roof boards underneath (between the purlins – a minor faff as they would need cut to size).
        This is only to reduce the height a little, and keep the barge boards fixed “downwards” which is my preferred option.

        Many thanks

        Tim 🙂

        • I would not recommend doing this as you are then putting the insulation inside the building. This can then cause problems with condensation. If this is the only way to do it make sure you create a void and vent it to allow condensation to escape. My preferred method is always to have the insulation on top of the roof.

    • Alternate to OSB I believe is marine ply. Think OSB would need to be treated. I believe a google search for warm deck roofs will provide a good selection of articles including one from rubber4roof from which I will be getting my EPDM. They also have some useful YouTube videos to guide you along…

      • You are correct regarding the Marine Ply. In my experience though I have never needed to treat the OSB. I like the Rubber4Roof site and it is cheaper than us for EPDM, they have a quicker delivery as well for it, I often recommend to customers to try them or even ebay for sourcing EPDM.

        Regardless where you get it from EPDM is the very best product to use on a flat roof.

  20. This is a great article and I’m planning on insulating a cabin extension soon. I recall cutting the insulation boards in my existing cabin and found this to be a pain to do. Been watching some youtube videos on cutting boards but great to hear your preferred technique. Afraid, no specialist table saws in my home!

    For the OSB boards I will be getting it from the timber supplier but they don’t do insulation boards.

    • I’m pleased to hear this article is a help to you. The best place for insulation boards is a general builders supply yard such as Jewsons, Travis Perkins etc.

      • Indeed but they come in standard sizes and I believe none will do any cuts for you like they may for timber.

        Thinking I will use my patio chairs as cutting horses, clamp a trim on both ends cut along with a sharpened wall paper remover. Well that’s the theory at least…

        • I do not know any company that will make the cuts for you. It is easy though, a timber saw or an old bread knife with cut through it easily as will a stanley blade for precision.

  21. Richard I am currently waiting for the arrival of my Justine log cabin and have started to look at insulation for the roof and floor. Is it the Celotex FR5000 that you would recommend?

    • I normally like the foil back board, it is the Celotex PIR (Polyisocyanurate) 50mm x 1200 x 2400mm. I have recently been told though that kingspan offer a similar board that has higher thermal performance so that maybe worth looking at too.

  22. Hi there, I have an Eila on order and am just finalising the insulation. I am using 50mm foil backed boards (celotex or similar). Can I stick EPDM direct to the insulation boards or will I have to board over the celotex with some ply or osb? Thanks, Tim

    • If you have a flat roof is is far better to frame it and put OSB or similar on top with the insulation inside. EPDM or the Roof Membrane will not stick well to just the insulation board.

  23. Hi I have just order foil board insulation for the roof . I have gone with 60mm and was intending to fix direct to roof and the the fix the shingles … I have just read down this post and see you have started to talk about framing and osb if the insulation is greater than 50mm. Do you see any issues if I don’t frame it with the 60mm board

    Regards. Jonathan

    • When you go over 50mm you’re asking a lot of the nails holding that depth of insulation, Also I’m not sure if you can get nails long enough. I would not use anything above 45 – 50mm thick insulation without framing and boarding the roof to make sure there are no problems.

      Of course though, it may well be fine, but it is not something I have done or could recommend.

  24. I’ve just managed to insulate and shingle one side of my Lotte roof but it’s now raining overnight and is forecast to continue tomorrow. The completed sides of the celotex (it’s not actually celotex but recticel, basically the same stuff) are exposed to the rain. Will it be ok?

    • I remember fitting a huge building that took over three days to finish the roof, it was the height of winter and during those three days we had snow, slush and rain on the roof with exposed celotex and it did not come to any harm, I have not used your make of insulation but I would imagine it will be fine if it is a similar material.

  25. We have a log cabin that uses 6 foundation beams that run in parallel rather than around the perimeter. If we were to insulate the floor then the insulation would be exposed at the edges. Is this okay or could water be soaked up through the insulation and into the floorboards? If I were to cover the gaps between the parallel beams would I need to put ventilation holes in?

    • Other suppliers do things a different way, I do not see why they use parallel beams and would suggest our method of a ring beam every time. But you have to make sure the base is to the footprint of the building and that it is flat and level. This will create a natural seal. A layer of DPC also helps with this.

      If you have parallel beams you will need to seal the edges, I would suggest infilling with timber the gaps. Make sure though your base is sealed. In extreme infested areas such as farms I have known customers to lay chicken wire in before applying insulation.

      Ventilation holes are only necessary if you expect water within the bearers caused by not using a DPM or a bad, none sealed base.

  26. Some of the videos I’ve seen show people fitting a wooden frame around the cabin roof and then fitting the insulation boards inside this wooden frame, would you recommend this? My concern is that if the insulation is open to wildlife on the side elevations of the ‘Royal Two Log’ cabin they may burrow in to it or peck at it and damage the insulation.

    • The Royal Two is an apex log cabin. If you are using 50mm or less then the side elevation and also the apex will be covered by the boards at the side and front and no entry should be made. You may though need to source slightly wider boards for the leading edge locally.

      If you are putting in thicker insulation then it is a good idea to cell the roof with framing and then a sheet of OSB / ply on top of that. The final roof covering would then attach to that.

      If you have a flat roof log cabin then is is also necessary to insulate in this way as the final roof covering will be felt, EPDM or roof membrane which cannot be fitted like felt shingles.

      The leading edge and apexes would finish as normal.

      • My log cabin has an apex roof. I was planning on using some 40-50mm insulation on the outside as previously mentioned and then put some good quality felt over the top. I notice though that above you say that would not be possible with felt only shingles. Why is that?

        • If you are using shingles these are very hard to fold over flat due to the thickness of them. Felt is far thinner and can be folded easily and trimmed. If you need to cover exposed insulation you can use a timber trim on the leading edge which is usual or raise / wider barge boards on the apex. But, if you wish to use felt under the roof shingles this can then be folded over. I have seen some people use this method OVER the leading edge trims as they will eventually rot as they are exposed and a felt folded over will protect them.

  27. Thanks for a very informative site:Regarding insulating the floor i have ordered a 27mm floor pack for my Stian which will be sitting on the composite foundation beams.I was wondering as the joist are 44m and fitting 50mm insulation will this mean that the boards will sit on the insulation with a 6 mm gap to the joists below.I was considering blind screwing using Lost-Tite Screw however will this not distort boards when fixing ?

    • If you are using 50mm insulation you will have a gap between the joist and floor board due to the joist height. However, the insulation we recommend is load bearing and the floor boards will sit directly onto this and supported by the insulation board, the joists are only there to secure the boards to and carry no load.

      I have not noticed boards distorting when nailed but I have not used the fixings you are referring to.

      Alternatively a thinner insulation can also be used.

      • I had the same concern when insulating my floor so I used 40mm celotex instead of 50mm just to make sure. However we are not planning on using the cabin in the depths of Winter so the slight decrease in insulation shouldn’t make too much difference.

  28. Thanks for you website – info is soooooooo helpful.
    I have a question about your method of insulating the roof – why do you not need an air gap between the insulation and the roofing material? Will condensation not then build up around the insulation and eventually cause the roof boards to rot?

    • Condensation can become a big problem when insulating under the roof boards, when it is on top I have never had a problem as the moisture build up is inside the building not on top of the roof. It’s been nearly twenty years since I have been doing it this way and I have not had a call back so far. But, I maybe wrong and others may have a different viewpoint or thoughts and I would be pleased to hear them if anyone thinks my personal method is wrong.

  29. How would you insulate the floor if building on a timber base? Confused were the DPM would sit, and if you put the insulation in the bottom frame, or if you need to build a further frame on top to add insulation & flooring?

    • If you are using a timber frame as your base then you would insulate between the joists that are integral to the base. You would not usually make a seperate frame as it would not be needed, the floor boards would then go directly on top of the joists within the frame. This is an example where the boards go directly on top of the joists within the frame.
      ” alt=”Floor joists within the frame” />

      But, there are no hard and fast rules on this, you can also put the floor joists on top of the frame as per this example:
      ” alt=”Floor joists on top of the frame” />

      In both of these examples the insulation would go between the joists.

      Regarding DPM the purpose of this is to stop ground contact and damp coming up through the ground. With a timber frame base you are already taking the building away from the ground so the task has already been accomplished.

  30. Hi Today I Insulated the outside of my log cabin roof. Didn’t want to use the rigid board as I am using part of inside as sauna. Obviously building in framing expansion method used insulation foil etc etc.
    Any way back to the roof. I figured after talking to the joiner across from me that there would be a risk of sweating between cold foil and hot roof, even in heated non sauna part.
    So I came up with this design. 47×75 on there edge all round outside, then every 600 I put 3 400 batons with a gap between them on there edge of course 75 up.After this I filled it with 50mm Rockwool flexi, this left me a 25mm air gap above. On top of the framing I put 18mm OSB 3. Then I fitted a 120mm x20 board in redwood from builders merchant round the bottom edge to hide the framing and match the cabin. After this I drilled through 25 mm holes aligned with the air gap above insulation and popped in manthorpe g952 round vents. It works a treat and is cheaper, more effective as it breathes and looks sturdy. Plus you have a solid base for your clout nails instead of bashing through insulation which sounds a bit too flimsy for me. I’m glad I spoke to the joiner before I started this. It’s more work but it’s definately worth it.

    ” alt=”Sauna insulation on log cabin roof” />
    ” alt=”log cabin insulation” />

    • Thank you for this information, it’s an alternative method for others to consider if there is a sauna inside. It could possibly be over complicating it but the vents are very important if you have an air gap.

  31. We’re thinking of getting a cabin for use as a garden office/den. Obviously we want it to be warm in Winter and cool in Summer with as little input of power as possible. Therefore insulating is important. I’m OK with doing the roof and floor but what about the walls? Probably will go for 58mm walls but how would you fit celotex to the inside? Normally I’d batten the walls, fit the boards inside and then clad but obviously if the wall boards can’t be fixed together this won’t work.

  32. Hi

    Will be attempring to insulate my Emma log cabin when it comes next week.

    Any tips for insulating a pyramid roof or are there any videos showing how?

    Do I need to install a breather membrane between the roof and 50mm celotex and batten round the edges?

    Kind regards


    • Using insulation on a pyramid roof is the same as an apex roof. You will need a deeper bargeboard or batten to conceal the insulation at the bottom the same as an apex roof. I do not normally use a breather membrane and have not come across a reason why this would be necessary on a log cabin roof.

  33. I will soon be insulating a flat roof with the EPDM sheet on a Yorick cabin. I have been wondering firstly is it worth using a vapour control layer over the deck before I put 75/100mm of polystyrene on and do i fix the insulation to the deck or just rely on the weight of the rubber over the top and… should i board over the top of the polystyrene? Thanks for your advice in advance!

    • For a flat roof it is better to batten around the side and then across the roof, infill this will your chosen insulation and then a board of OSB or similar is fixed on top. The EPDM is then glued to the board.

      • Hello Chris. Have you done your roof insulation? I just got York with EPDM and was wondering exactly the same. Which type of insulation you went for (or was it the polystyrene mentioned) and did you use any vapour control?

  34. This is a great guide, but I have one question. Once you’ve put the celotex on the roof, do you need to board over the top of it with OSB or similar before laying the felt or singles?

    • If you’re using 45mm- 50mm it’s not necessary to board it in my opinion as the nails will go through to the roof below and still provide a good fixing. If you’re using anything thicker then the roof would be battened and OSB or similar would go on top to enable the final covering to be fixed.

        • I’ve recently done this with 50mm celotex and it’s a perfectly good method. I ordered 70mm clout nails and the only issue I found is that as you’ve covered up the boards with insulation you can’t tell where the nails will come through, so you sometimes hit the T&G joint between boards and can see nail points in the joint underneath (if you’re unlucky enough to hit them exactly). If I were doing it again I’d go with 65mm clout nails.

We'd love your comments on this.....