Expansion in Log Cabins

Two Extremes with Log Cabins

There are two extremes of the year in a log cabins first year of life; The height of Summer and the depths of Winter. Both of these times may possibly cause problems for you depending on the level of treatment you gave your cabin when you installed it. These problems will generally only be noticeable in the first year cycle of a newly built log cabin as I explain in the articles referenced below.

The problems are one of either expansion or contraction of the wall logs that make up your log cabin.

But, with that said you should never, ever notice this movement, such is the design of most log cabins. The building will grow and shrink un-noticed by you…..

BUT ….. only if it has been built, treated, and vented correctly and also with the correct layer of damp proof membrane on top of or within the base. The correct treatment though cannot be stressed enough, as it will inhibit both these natural features of wood and you will never have a problem or even notice what your log cabin is doing over the seasons.

Contraction of logs in your log cabin – Summer

In the summer we will see contraction and I have written a lot about it in a previous article: Moisture Content of a Log Cabin and Depth of Treatment this article is helpful as it explains the intake and expulsion of moisture from the relative humidity and explains how each log can expand and contract by as much as around 3 – 5mm per log. Over the course of a building log height you have a potential movement of about 80mm, that’s about 3 inches! Sometimes it will be more if the building has received little or no treatment and within its first 12 months of being installed.

A second article which will interest you on the subject of timber movement within a log cabin is: Contraction of a Log Cabin this article explains what can happen in the height of summer, and when a log cabin has had little or no treatment.

Expansion of logs in your log cabin – Winter

Here are some examples of problems that may occur, all of which are down to the natural expansion of timber within the winter months, most of which could be avoided with treatment, damp proof membrane and in some cases ventilation and correct installation of your log cabin.

White bits:

The most common area that you will notice with expansion in your log cabin is when white bits start appearing.

Classic winter expansion of logs in a log cabin – notice the bare wood appearing above the door fascia

Expansion of the logs has caused bare wood to appear from behind the window fascia

For log cabins built around July, August, September and a little later this is fairly common to see and is entirely normal. This is happening as the logs are inherently a sponge and made up of 1000’s of straws which of course the tree used to suck up water from the ground, this is what is happening with the logs during the winter months, they are sucking in moisture and expanding.

This is entirely normal and one that can be easily inhibited by the correct application of a good quality treatment. We also advise in our Log Cabin Treatment Advice article that when treating your log cabin to also paint behind the fascias to the side and above and you will then never notice this expansion taking place at all. If correctly treated it may not even take place at all!

Wood is made up of 1000’s of straws, all of them are designed to suck up moisture from the ground. In the correct treatment of a log cabin our aim is to block these straws as much as possible to inhibit the natural expansion and contraction

Gaps Appearing

During the summer months we can sometimes see gaps appearing if the cabin is not treated well of built correctly. During the winter we can very occasionally see another form of gap appearing and this is generally above the door.

A gap has started to appear above the door as the logs have expanded so much the contraction space has started to appear.

We have seen this a few times in extreme cases, this is very easily solved with a shim placed under the door and the checklist at the bottom of this article followed come the warmer months.

Frames Apart

In our Log Cabin installation advice page and also the instructions that come with all log cabins we do try to get across the importance of NOT fixing anything across two or more logs, including the doors and window frame and fascias as the wall logs need to be able to move independently due to their contraction and expansion. Sometimes though this advice is not followed.

If door or window fascias are fixed to wall logs you can see the expansion of the logs may force the frames apart – never fix log together or inhibit their natural movement!

Fixing fascia that are attached to the top logs to the door frame can be pulled apart by the expansion force.

This door frame is being pulled apart as the top fascia has been fixed to the top wall log, as the logs expand the top part of the frame is pulled upwards by considerable expansion force.

Below is another good example of the door frame being pulled apart from the top fascia being fixed to the wall log. See how evident the rogue screw is, as well as how much expansion has been caused from the force the screw has created:

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Floor and Roof

The floor and roof of your log cabin is also affected by expansion and contraction and as we advise it is important to consider the time of year you are installing, at the height of summer you will need to ensure you leave a small expansion gap between the boards. In the case of the floor it is very important to leave room for expansion all around so the floor does not push against the sides of the log cabin.

It is very important to leave an expansion gap all the way around the floor as highlighted in our installation advice, this will then avoid a roof, or floor, from rippling when the winter comes.

Treatment

It is always at this time of year that we get a series of complaints that all can be traced back to treatment, I wrote this article at the same time last year: Log Cabin Treatment Gone Wrong this highlights a lot of the issues when treatment is not correctly applied or the good quality treatment used.

Log cabin treatment gone wrong

If our advice has not been followed regarding treatment it is the height of winter when it will become most obvious.

Problems with treatment will not only manifest itself by unsightly marks as above but you may also have leaks in extreme driving rain conditions. The is due to ineffective or cheap treatment being used which then cracks and allows water to ingress via capillary action. This can also be caused by treatment not being applied correctly, particularly one of the cheaper shade treatment requires light sanding, wiping with spirits and at the least two coats applied within a few hours to be effective, the manufacturer goes on to state that with dry wood three coats should be applied, it is often overlooked as well that a wood preservative is required under many cheaper treatments. Without following any manufacturers explicit instructions any treatment will be ineffective and problems during at least the first year of a log cabin life can be expected.  We would recommend at least four coats of any treatment correctly used. For more advise on this please see: Log Cabin Treatment Advice.

Water Ingress

There are a number of reasons for water ingress, the most likely is lack of treatment, a poor quality treatment or an ineffective treatment, especially in the corners and importantly on the end grain, this is particularly important to stop tracking of water via capillary action via the grooves in the profile of the logs.

Capillary action can allow a weap to follow the logs in a building that has not fully settled or been treated carefully in the corners, tongue and groove or the end grain.

Little or no treatment has been applied to this log cabin. Water marks are now becoming evident in the corners and some mould build up on the door.

As I have mentioned before. Wood is made to act like a sponge. If it is not treated correctly it will absorb water by its nature. This door did not receive a very good level of treatment and over the course of a year has absorbed a lot of water. A great deal of this could have been avoided with a good treatment and of course ventilation within the cabin if it is closed up for long periods of time.

Until a building has fully settled over a period of a year and gone through it’s various cycles it is possible to have driving rain force into the corner joints. BUT, this is very easily prevented by the correct application of a good quality treatment as all the joints are sealed.

Water ingress along the bottom few logs pushed via driving rain. A good quality treatment correctly applied prevents this. I have noticed that some pictures of issues will show this area more often. As can seen from a treatment picture further up this post the lower part of the cabin is missed, possibly as it is harder to treat due to bending over? It may also be that this area takes more driving weather? I think though from experience it would be a good idea to concentrate on this area if you think the log cabin is exposed when you treat it.

Condensation

Condensation is occasionally overlooked and this can affect your building greatly. As we advise it is vitally important that a damp proof membrane is incorporated within your base on top of it. Advice on this can be found in our Log Cabin installation advice article.

Even with a DPM, condensation can still build up in your log cabin if it is not regularly used, in this case it is highly advisable to fit some sort of vent. More advice can be found in our Ventilation in Log Cabins article.

As well as ingress from outside it is possible for condensation to build up inside a cabin if not regularly used or ventilated.

Condensation can also manifest itself as damp spores on the roof and walls. This is a mild case but the building does need some sort of ventilation when closed up for long periods.

On a larger scale, especially when a DPM is not fitted so much moisture can be built up it actually looks as if there is a leak in the roof. Ventilation will resolve this problem.

Doors and Windows

Last night I had an email from a friend who said ‘don’t go around the back to the conservatory door as it’s stuck, it’s always like that when its cold’. I smiled to myself, of course it has nothing to do with the cold, it’s everything to do with treatment and inhibiting the expansion of the wood in her patio doors. It’s exactly the same with a log cabin door set and windows, they will react in exactly the same way if they do not have enough layers of good quality treatment applied.

Doors and windows, if not treated well enough and certainly within the first year, may expand and could become tight in the frame. Ideally doors and windows should be treated both inside and outside to guard against expansion and contraction which can in turn cause warps in a frame

Summary of Expansion in your Log Cabin

All the above points affect any log cabin no matter the manufacturer and indeed any timber structure both inside and outside of your home.

If you have any of these issues, please do not worry, they can all be solved easily.

  • White Bits: This is the easiest to solve, wait until the weather improves and then remove the fascia, you can then paint behind them and you will never notice this again.
  • Gaps appearing above your doors or above the windows. This is easily solved by raising the door or window frame and then inserting a packer the length of the frame. The gap will then be hidden behind the fascia. You will need to remember you did this and consider removing it in the Spring when the log cabin starts to contract again.
  • Frames or trim parting: It is very likely that fascia or frames have been attached somehow to the logs. Please remove any fixings you can find. Doors and windows can easily be removed by taking off the fascia, please then make sure the whole frame is refixed together and reinstall. Do NOT fix any part of it to the wall logs or trim mounted on the corner triangle (in the case of corner log cabins)
  • Floor and Roof: This will be a little trickier to solve. For the roof I have found more nails can be added and it is generally enough to solve the problem as it can still expand across the whole length. The floor maybe pushing against the wall logs, check for this and if it is the case you must create an expansion gap all the way around. A jig saw will be able to accomplish this. In extreme cases you may need to consider a whole new replacement floor.
  • Water Ingress: This one is a little trickier during the winter months and it is probably best to leave it until the warmer Spring months. You will need to review your treatment process and what you used. For cheaper shade treatments you will have sanded the walls, washed it with white spirit, applied a preservative, then applied at least three coats in batches of 4 – 5 hours. Better treatments such as Sikkens and ours will generally need three coats, sometimes an undercoat is also required. For our carefree protect treatment this can be applied direct and built up to three – four coats over a number of days for full protection. Make sure you have read and fully actioned the manufacturers instructions. Please see our depth of treatment article for more advice. You will need to consider re-treating your log cabin and also upgrading the treatment you originally applied. As we advise, if you use a top quality treatment, correctly applied these problems are unlikely to occur. The first thing, by eye you can notice if a treatment is a good quality is ….. is there stretching of the treatment across the joints over the winter? You can often see this, a cheap treatment will simply crack and that is when ingress can occur through capillary action. Look out for this!
  • Condensation: Please check an effective and un-punctured DPM has been applied within or on top of your base. This is your first port of call for a condensation problem. If you are not sure or one has not been applied the floor will need to be lifted and one fitting. If it has and the building is closed for long periods over the Autumn and Winter please consider adding at least one vent into your building. More advice can be found here: Ventilation in Log Cabins
  • Doors and Windows: On most of our log cabins the hinges can be adjusted to account for this, please see this page for advice: Log Cabin Doors you will also need to consider the treatment advice above, ideally doors and windows will be treated equally both inside and outside.

First Year of Life! 

It’s odd but after a year and completing the cycle a log cabin seems to settle down a lot, I think it is because the straws in the wood make up has dropped, crushed or have been blocked, after a year all these things seem to settle and almost disappear.

Some of the above may have left marks or stains which take away from the aesthetics of you building, however, all is not lost and can be easily cleaned again, please see this page for advice: Cleaning a Log Cabin

Dealing with Expansion / Contraction in Log Cabins

We know that Log Cabins move and certainly within the first year of life they can move quite a bit. I explain this in an article about moisture content in log cabins which greatly effects the expansion and contraction of the wall logs.

The trouble is this movement can be a bit of a problem if we want to put things on the wall, or perhaps adding some shelves or fixing machinery. You may even want to partition a portion of your cabin for several reasons, perhaps you want a shower or a toilet or just a separate storage area. You might also want a thinner log building due to your budget but you would like to insulate the walls to use it as a garden office.

All of this can be done easily but to do so we need to keep fully in the front of our minds that the bloomin’ thing will move and we don’t want to stop it.  If we do inhibit this natural movement we can end up with all sorts of horrible things happening such as:

  • Splits in the logs – This will normally be caused by logs being held together
  • Gaps appearing where logs have been held – normally by a window frame being screwed to the logs
  • Moisture entering through gaps and splits

To avoid all these problems, if we want to fix anything to a log cabin wall this is the simplest and best thing to use:

Expansion Slat for Log Cabins

Expansion slat for use in a log cabin to still allow movement of the logs.

Expansion slat for use in a log cabin to still allow movement of the logs.

This is a handy bit of wood and you can make it out of left over floorboards or roof boards. Any timber will suffice though and you will pick the thickness depending on the job you want it to do.

I often advise customers to make these for use as storm braces when they are in exposed locations, off cuts from the roof or floor boards is fine to use and you then position them behind the corner interlocks so they’re not really seen. This slat will then be fixed to the top most log and the bottom of the slat to a lower log, this then ties the whole cabin together.

The very simple principle here is that we have one fixed hole at the top and slots in the middle and end (depending on the length). The top hole is screwed tight and using a washer the slot fixings are not tightened fully so we can still allow the logs to move behind the bracket.

Shelf Fixing in a Log Cabin

Using this system you can put up shelves, cupboards and fix tools to the walls:

Expansion slats for fixing things to the walls.

Expansion slats for fixing things to the walls. Using this slat will allow the logs to still expand and contract.

You will see from my diagram that we are fixing the shelves to the expansion slat and not to the logs. For heavier duty uses you may want a thicker slat and you may want to bolt it fully through the log cabin wall.

This is also needed for securing cupboards to the walls and especially useful for electricians when securing a consumer unit.

NOTE: in the first month or so a log cabin will settle quite a bit from first being erected so it’s best to leave it for a few weeks before adding brackets and securing fittings. Within the first year the cabin will move the most as the wood needs to ‘die’ a little more. Year two will be a little less. Years three, four and onwards the movement is hugely reduced. Also remember the most important thing with a log cabin is to properly treat it. Proper treatment with a good depth of treatment will greatly inhibit the natural contraction and expansion and reduce it to a minimum. More details on Treating a log cabin

Partition Walls in Log Cabins

The same as you do in your home you may wish to put a partition wall into your log cabin for any number of reasons. You can do so as long as you remember the log cabin is always moving!

Using the simple principle of the ‘expansion slat’ explained above we can create slots in framing and make a wall as any stud wall would be made remember though the slot fixing should not be fully tight and always allow the logs to still move in both contraction and expansion.

Partition wall framing in a log cabin

Partition wall framing in a log cabin

You would make a partition wall as you would any stud wall and probably with noggins for extra strength. Your final surface covering could be anything you would like including plasterboard. However, if the floor has already been laid do not fix it to the floor as like the wall logs the floor will be expanding and contracting as well.

Twin-Skin Log Cabins

You may have seen twin skin log cabins in the market. I’ve put a couple of these up and they really are a challenge and I don’t like them for a number of reasons. Mainly the design intent is all wrong but I will not expand further here. If you require my personal thoughts please feel free to ask me.

Instead of a twin skin design I prefer making an inner wall and one that is independent to the main log cabin wall. This is particularly useful if you are constrained by your budget and want an insulated log cabin but don’t want to opt for thicker logs.

Also, if you are obtaining building control approval because you intend living in the cabin then it will need to be insulated to building standards. Thicker logs certainly help with insulation but sometimes a control officer will want more. I’ve been involved with several projects and a building officer will often ask for 50 – 100mm thick insulation in the walls (depending on the log thickness) and 100mm in the roof with 70mm in the floor. The roof and floor is easier as I make mention here: Insulating the floor and roof of a Log Cabin.

It’s completely fine to add an inner wall to your cabin and fill the cavity with insulation as long as you constantly bear in mind that the logs of the log cabin itself are always moving as previously explained.

NOTE: Also though consider what you are going to do where the logs join the roof, we cannot restrict the contraction and if the cabin is dropping over the summer if you have not allowed enough room the roof could end up sitting on your internal frame causing a gap to be formed.

Allow for the contraction as well as expansion!

This explains how you can create an internal wall to allow insulation inside the log cabin:

Creating a twin wall log cabin

Creating a twin wall log cabin using the same expansion slat principle

Using the same principle with the expansion slat we can create framing internally against the wall. The frame will of course depend on the depth of insulation required but employ the same methods and remember the logs need to move independently.

Building control will ask for a breathable membrane, followed by a small air gap, and then the insulation in between the frame. On top of the frame you will place your surface covering. Timber logs of 28mm looks good or use a thinner cladding for economy or perhaps plasterboard for a smooth sleek, modern finish.

I normally like to insulate the roof on the outside and this can still be done if you are lining the walls on. The reasons I like it on top of the roof is:

  • It’s generally easier and quicker
  • It’s less expensive
  • No cavity is formed to collect condensation

If you are cladding the inside in timber and putting insulation on top of the roof you will still maintain the look and feel of a log cabin and benefit from the space the vaulted roof provides.

This is an example of insulation on top of the roof:

Insulation added on top of the roof with inner wall insulation

Insulation added on top of the roof with inner wall insulation

Make sure you allow enough room for contraction. With this example you can see I am keeping the inner framing below the roof boards as with contraction there is a chance the boards could sit on top of the frame making the wall logs  separate.

I’ve used a fascia suspended from the ceiling that will sit in front of the inner wall but is not connected to it allowing it move up and down as the log cabin expands and contracts. Fill any cavity created with fibreglass insulation wool so it can also move.

In a previous article on roof insulation I was recommending 40mm – 50mm thick insulation.  If you are going to use thicker which you may want to, you would need to ‘cell’ the roof and board on top of the insulation:

Using timber framing to cell the roof and infill with insulation boards

Using timber framing to cell the roof and infill with insulation boards

Some building control officers will ask for 100mm in the roof. To do this you will need to create a tray on the roof, then cell the tray and put in the insulation board with a final board on top and then the final roofing material. You may also wish to consider adding a breathable membrane.

If you wish to insulate under the cabin roof you could so within the purlins and then clad underneath them:

Using insulation in between the roof purlins

Using insulation in between the roof purlins

Another method you could consider is as follows:

Creating a ceiling within a log cabin

Creating a ceiling within a log cabin

Again like the methods above we are making sure there is enough room for expansion and contraction of the outer wall logs.

Please remember, if you create any voids to really consider venting them as a buildup of condensation can cause huge problems.

Summary of Dealing with Expansion in Log Cabins

Log cabins are an extremely versatile building and are very inexpensive and they can be used for any number of uses from a humble garden shed all the way up to full blown family accommodation.  They will all behave the same and will all move all the time. So long as you remember and allow for this you can do anything you want to them. Including partition walls and internal insulating walls as I have shown.

Please Note: These are ideas for you to take away and use how you will, these are not detailed plans with measurements and the drawings are NOT to scale. If you go on to carry out any of these ideas please let me know how you get on but this is not a simple DIY task and you will need some knowledge and understanding of the processes and materials involved.

One last thing; the windows and doors are also part of the outside wall so don’t join any of your internal framing to the doors or windows in anyway, treat them exactly the same as the logs.

Please ask me any questions you have on this or if you do use my ideas, please let us all know how you got on. Like the timber frame bases for log cabins none of this has a hard and fast rule except: Log cabins;  Move!