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.

As of recent, we have also started selling Insulation Kits for Log Cabins. These include all of the necessary materials needed to insulate both the roof and floor of your Log Cabin. While we do offer these kits, you may want to buy your own insulation supplies from a local builders merchant- I’ll explain what’s needed for you to do this along with advice on how to insulate your log cabin ready for the colder months.

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 Guide

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.

More on Log Cabin Insulation

I was sitting here this evening enjoying a glass of wine as unfortunately I am in the habit of doing. I was having a wander around the internet just to see what other competitors are up to at the moment.

I then saw a statement that said ‘Very few other companies even offer floor insulation with Log Cabins’. It made me choke on the current mouthful of wine I was enjoying. In fact that mouthful pretty much covered my keyboard with all the spluttering.

I had to re-read exactly what I had seen to be sure. Yup! It did actually say  ‘Very few other companies even offer floor insulation with Log Cabins’. I then had to write this as a bit of a rant as I was flabbergasted this statement was being used to sell a log cabin.

Rip Off

Please let me explain and for you to watch out what you are buying.  I have been involved in numerous companies within the garden and log cabin industry. One of the top things they all did was buy the insulation from a builders merchant or similar supplier. They would then add 30 – 50% and sell it to the customer as an ‘insulation pack’. In a previous life of mine we would order the product from Travis Perkins and have them deliver it on the same day as the cabin and make 30% on it. Companies try all sorts of packs and give all sorts of recommendations and up-sell. In my mind it is all very dishonest to the customer.


Since I joined Tuin and Tuindeco that was one thing I stamped out. I felt all we should be interested in is selling our primary product, it did not sit easy with me at all that we are basically ripping people off so when I joined I quickly put a stop to ‘insulation packs’ with our buildings.


My advice, whether you buy from us or not, is DO NOT buy any insulation packs with a log cabin.  You will find everything you need at a builders merchant or on-line from people who specialise in insulation, they are in a far better position to advise you on the most suitable product, there are loads of different products available. I had a customer recently who found insulation boards that were 20mm thick but the same U value as 100mm standard insulation board!

The only thing you will need to do, to fit insulation is some extra timber for barge-boards and covering, ask me please if you need this.

I really don’t mind who you buy from, (slightly miffed if it’s not us of course) but I will offer advise to anyone who needs it on how to insulate their log cabin very cheaply, Of course also without falling for the ‘log cabin insulation pack’ trick. Including how to insulate the inside of the walls and line them so you don’t have to fall for the double skin log cabin trick, which is a subject for another post, and PLEASE don’t get me started on the double glazing in everything trick!

Here’s a post I wrote about insulating a log cabin a while ago which may be interesting to you:


Ah but you might like the easy life? Of course Sir,you would like an insulation pack?  Yes Sir we can of course provide that …. it’s really great, U value Blah, it has Poly blah, blah, it’s really good honest Sir and very good value

All I’ll do is give the local building supplies a call or maybe on-line and order it for direct delivery on the same day as I deliver you the log cabin…. But hey I can make some money from you … card details please.  Do you really want that? …. Nor do I, I believe in honesty and ‘log cabin Insulation packs’ are the biggest rip off in the trade at the moment ….. oh and twin skins …. oh and double glazing in everything … I said NOT to get me started!!