Base requirements for Log Cabins

Log cabins are not built like a shed,  at least the good ones aren’t.

What I mean by this is;

Sheds:  When a shed is installed the floor is placed down first, the walls go on top of it and the build is continued.

Log Cabins:  With the majority of log cabins, the cabin is first built and the floor goes in afterwards and sits within the cabin and is not an integral part of it.  The floor system is known as a ‘floating floor’ and should not actually touch the cabin walls although the floor joists may be and more often than not are attached to the log cabin foundation beams.

A normal Shed is built on top of a floor with joists underneath it

A log cabin is built around a perimeter foundation beam, the floor joist and floor will go in after the cabin has been built.

Foundation Beam.

All our cabins are built around the perimeter of a base and it is prefered that it is built on a foundation beam.

As standard we supply 70mm x 44mm tanalised beams.  These are supplied to go around the perimeter of the building and to sit between the first log and the base.

Using these gives your first layer of logs protection from sitting directly in any water.  If you would like something a little better we also have, as an option, profiled foundation beams.

These are supplied with all our cabins and go between the base and the first log around the perimeter of the cabin
Tanlised foundation beams.  These are supplied with all our cabins and go in between the base and the first log around the perimeter of the cabin.
These beams are profiled to allow any water to be flushed away from the first log. Available in tanalised and hardwood
These beams are profiled to allow any water to be flushed away from the first log. Available in tanalised and hardwood
The same as the ones above but these ones are made of a composite material and will never, ever rot
The same as the ones above but these ones are made of a composite material and will never, ever rot
The foundation beam runs around the perimeter and underneath the first log and acts as sacrificial timber and ensures the first log is kept away from any wet

Perimeter

Understanding the above you will realise that all of the weight is on the perimeter of the cabin.

When constructing a base consideration should be given to this.  Sadly I’ve been to several fits where the centre of the base is great but the edges are all chipped and drooping where the shuttering has been removed as all the concentration had been placed on the majority of the base with an eye to shed building.

The greatest strength for a log cabin base should be within the perimeter as this is where all the weight is.

Level

Our Log Cabins are extremely precise things, the best machinery is used to mill the timber and as such there is little tolerance. They are designed for each log to sit directly on top of one another and are interlocked in the corners via corner connection and the tongue and groove connection along the log.  They are designed to withstand vertical forces, they are not however designed to withstand any lateral forces.

It is quite often tempting for a landscaping / building company, as they are used to doing with patios, to add a slight incline to the base to help with drainage.  They tend to do this as a matter of course without consultation and are really chuffed to tell you that you have a 2 degree incline!

This is really not very helpful as in effect you’ll be building your cabin on a slope and subjecting it to the lateral forces simply from gravity.  A cabin is really not up to handling gravity and the subsequent sideways force it puts upon it when on any sort of slope.

The end result will be a buckling and warping building and most certainly it will feature split and strained logs over time and of course the inevitable tears as you see your lovely building disintegrate over time.

The biggest thing though about an unlevel base is that it makes it bloomin’ hard to put the thing together, fully expect all sorts of problems with a wonky base:

  • The logs won’t seat properly.
  • The windows or doors will be on the huh.
  • The apex will not sit flush with the upper wall leaving a gap which you will then have to trim to look anything, either with a planer or bits of wood stuck on it.
  • The roof boards will not go on straight and there will be an incline in them which looks terrible and you will always notice it.
  • Long term problems with warping, twisting, straining, cracking and splitting.
  • You’ll be on the phone to me immediately during installation as it’s not going together  or in about 3 months time when it’s falling apart.  I’ll pop out and look at your base and tut a lot, we’ll end up arguing and you won’t even offer me a cup of tea!

What if the base isn’t level?

Sometimes we have to use what we’re given or that which is already laid and there’s not often a great deal we can do about it.  Trying to add a screed to a concrete base to get it level rarely works and will simply fall away as pressure is put on it.

If the base is out we have to do something about it before the cabin can be built, either it’s demolished and started again or another solution needs to be found.

When I fit, which isn’t often these days I carry a box of ‘slithers’ of pressure treated timber in my van of various lengths and depths. Using these I could often overcome any deviation by adding them to the foundation beam and ‘chocking’ where necessary.

However, if you are going to chock a cabin up for goodness sake make sure it is supporting the whole length and not just a corner.

Here’s an example:

poor-log-cabin-support

This was a log cabin ‘gone bad’ I recently visited to help sort the poor thing out.  Its a bit of a long story but the customer had some particularly shoddy builders in to build it for them who neither cared nor had a clue what they were doing and this was a substantial and very expensive log cabin.

The above image shows their version of chocking up the corner to make up the deficit in the unlevel base.  This piece of plywood doubled up was supporting the corner of a huge 70mm log cabin.  Not only had all the logs sagged across a 1m stretch the corner joints were also badly damaged and did not fit as it was still badly out of level.  The apex was also ripped apart and don’t even get me started on the purlins.  But if it had worked –  the plywood would have rot within a year and the whole thing would drop and destroy the cabin anyway!

Here’s how it’s best done:

good-support-logs

I took the building down for the customer and reassembled it correctly and this is how I chocked the fault in the base, notice I am using tanalised timber and that it is being supported along it’s length and kept properly level.

So, with a trusty box of slithers of tanalised timber most unlevel areas can be overcome just make sure you have several depths available to you.

Please though, use timber that isn’t going to rot in five minutes and make sure the foundation beam is supported throughout its length and, importantly, make sure the building is completely level in both planes regardless what you do.

Footprint

All Tuindeco log cabin measurement are taken from one end of the log to the other, so a 3.0m wide log cabin is exactly that, from the outer edge of the log to the outer edge is exactly 3.0m.  The base doesn’t specifically need to be to this measurement as all the logs have a crossover connection, this is generally 100mm or less depending on the size of the cabin (please ask us for your particular building).

So, for instance the base actually needed for a 3.00m wide log cabin is:

  • Length of log – 3000mm or 3.00m
  • Crossover – 100mm

Log – (crossover x2) = 2800mm or 2.80m

In this example we could make our base at exactly 2.80m wide and the log cabin will fit on it exactly.  Be careful though, there maybe a wiggle in the shuttering or somebody is not as exact as they could be, there’s no room for error when doing it exactly to the footprint so it might be wise to add a centimeter or two either side just in case.

If it can be done though I think it looks far nicer, it also has the advantage that when it rains water does not hit the base and fly up and make your lower wall of your smart, new log cabin all dirty and mucky.

Water and mud splashing up on the logs because the base is bigger than than the footprint

Another good idea when making the base to the size of the footprint is to then add a French Drain, this looks really nice and also absorbs the water, stopping it splashing up and also removes the need for guttering.  The other advantage is the loose stones can then cover any of the concrete you don’t want to see.  Apologies this isn’t a log cabin but I’m sure you get the gist:

French Drains are very useful around a log cabin base

Log Cabin Base Requirement Summary

A base can be pretty much made out of anything and we’ll get onto that in a moment but any base provided for any log cabin has to follow this criteria:

  • Consideration should be given to the majority of the weight being placed on the perimeter of the cabin.
  • Consideration should be given to the weight of the cabin, a 19mm is obviously considerably different to a 70mm.
  • It should be 100% level in every direction.
  • Ideally it should be square.
  • Ideally to just over the footprint size of the cabin.

Type of Bases

I hope with the above waffle I’ve given you a little idea what we’re ideally looking for in a base for your new and sparkly log cabin.  I’m not going to go into how to build a base as I’m not a builder or landscaper, nor would I want to be as it looks like jolly hard work.  I will however give you a few examples of what can be done and used.

Concrete

A base of concrete can be done in a number of ways.  Generally it can be done with simple timber shuttering.  The average base will be about 80 – 100mm deep.

Simple concrete base with timber shuttering
Simple concrete base with timber shuttering

Concrete Blockwork

We can also get a little more complicated with a block work supporting wall and then filling with concrete, perhaps reserved for the bigger buildings that needs a little more weight supporting structure around the perimeter.

If you’ve got a large building your landscaper or builder may advise steel reinforcing within the base itself, remember though not to forget the perimeter.

Steel reinforcing within the concrete base
Steel reinforcing within the concrete base

For advice on mix ratios, strength of concrete etc I’m afraid I’m not the one to ask, there’s lots of advice across the net and it’s probably best you sought that information elsewhere.

However! If i’m pressed to offer my very basic advice from experience use a mix of one bucket of portland cement to five buckets of ‘all in 20mm’ ballast gravel and add the water slowly, don’t make it too wet though, it needs to be a workable fluid, keep mixing until it’s uniform in colour.

As a rule of thumb calculate the volume you require (LxDxB) and add one third.

Creating the base is pretty straight forward, use timber board as shuttering to guide the edges, mark out the area and use a tape or string corner to corner to ensure it is straight.

Level the shuttering with a spirit level and pour your concrete.   Keep working it across the surface with a board until it is level with the top of the shuttering boards.  Allow it to set for three or four days and et voila your base is formed.

Alternatively; ask someone who know’s what they’re doing.  The above concrete method sounds good in principle but I’ve never managed to get it right and still had a few undulations in it, depressions are fine, hills aren’t so good!

Slabs

This probably doesn’t even need an explanation as it’s very cost effective and pretty simple to lay.  Again like concrete follow the base criteria I mentioned.  Normally a 70mm layer of dry sand and cement is sufficient, tamped down until level with the slabs then levelled on top of it.  A quick method and probably the cheapest and can work for most of the cabins we sell.

This I can get right and is pretty straightforward, just make sure it’s all level.

I have in the past tried the various other ‘eco’ slab bases but I could never really get on with them, they were more expensive than a simple concrete slab and still required the same amount of levelling, I still remain to be convinced of their real benefit and hope to be one day.

Timber Frame

This is by far my favourite method of laying a base, of course it’s not the best way I just enjoy doing it as there are so many permutations and challenges.

It’s using a timber frame supported by stilts, or pads or simply paving slabs positioned at intervals.  I find it a good environmentally friendly solution and great for areas where concrete is just not possible or when there are steep inclines to overcome.

There’s no hard or fast ways of doing it so I’ll simply give you a few examples for ideas:

A Stilt base, great for air circulation and to be flash you can say you are adopting the principles of Walter Segal

Example-frame-base-for-log-cabins

Timber frame on a bed of shingles

Timber Frames

The perfect way of building a timber frame base. The first foundation logs have been added.

The perfect way of building a timber frame base. The first foundation logs have been added.

Timber Frame Base

Square and level is the key!

What I love about a timber frame base is that:

  • It can be moved.
  • It’s truly a temporary structure which is great in certain circumstances.
  • It allows air flow and therefore the timber will never rot even if it’s not treated.
  • It’s a cheap solution in inaccessible areas for concrete.
  • Cheap overall.
  • If subsidence occurs you can simply jack up the area concerned and re-pin.
  • A good system when flooding occurs naturally and does not affect it’s environment.

To make leveling the base we do have a nice product. It’s not a bad price either and you can level between 30mm and 140mm using a combination of two units:

Very useful pads for easily supporting and leveling a timber frame base for your log cabin

Very useful pads for easily supporting and leveling a timber frame base for your log cabin

Please also see a recent post about a customer’s building for more examples of a timber frame base for log cabins:

Log Cabin Base Construction Summary

I’ve missed out loads of other ways, one of them being a brick or block plinth such as this:

Block Plinth base

There’s also systems on the market such as this:

Jackpad system of supporting a timber base frame

Pad supporting timber frame on a log cabin

There is truly a myriad of systems out there to form a base for your log cabin, much of it is down simply to cost and then personal preference and of course convenience, more than likely I’ve confused you more but no matter which method you pick:

If you want to be able to install your log cabin easily and then have it last for year and years then the base must be to the following criteria;

  • Give consideration that the majority of the weight is being placed on the perimeter of the cabin.
  • Give consideration to the weight of the cabin, a 50mm base is not going to cut it for a a huge 70mm beast of a building.
  • It should be 100% level in every direction and this is THE most important factor
  • Ideally it should be square.
  • Ideally to just over the footprint size of the cabin.

Just one last thing for you to consider and a bit of advice, if you’re opting for a concrete or paving slab base think about adding a damp proof membrane either within it or on top of it, this will then stop any damp coming up and impacting on your log cabin during the winter months.

I hope this has helped, feel free to comment or contact me if i can help further especially with the timber frame bases as I really enjoy these and love seeing them used in tricky situations.  For advice on the slabs and concrete bases it might be better to ask a builder!

UPDATE: Here’s various diagrams I have since added to other posts that may also benefit the reader of this post:

Advice on using a Damp proof course in your base.

Advice on using a Damp proof course in your base.

The base configuration when using our profiled foundation beams.

The base configuration when using our profiled foundation beams.

Insulation in the floor

Insulation in the floor and foundation beams.

Decking – the usual method

I’ve been asked a lot recently about our garden decking and especially how it is installed and on what sort of base, so I thought a short guide maybe helpful to our customers.  Of course it’s also a plug about our products, our composite decking is proving very popular as are our decking tiles and decking boards.  Interestingly sales  for the composite decking is increasing month on month

Composite decking

Composite decking

As a quick guide I suggest the following, of course there are lots of ways of accomplishing the same thing but this, I hope, is a good guide or at least gives you a few pointers.

Planning

Like any project, planning is the most important part, it shouldn’t be overlooked, what’s the old saying?  The five ‘P’s’:  Planning Prevents Pi – –  Poor Performance!

So, first make a rough drawing of your design, laying out pieces of wood to mark the edge of the planned decking always helps me to visualise how it will look.  Decking board at right angles helps to draw your eye into the house, board’s parallel show off the width of the decking.

It’s a good idea to make a scale drawing and also add the house walls, openings, obstacles etc.  If you’re attaching the deck to your house always make sure that the attachment point is 150mm below the damp proof course.  Make sure as well, you allow access to inspection covers and importantly don’t block air vents.

Measuring

Using your scale drawing calculate the area of the deck.  Divide the area of the deck by the size of the decking tiles you are using or the timber / composite decking planks.  Remember you will have to include spaces for expansion and drainage between planks, I tend to use 5mm as a guide.

If you need help calculating what is required please do contact us.

Ground Work

Decking is usually built on a framework supported by concrete footings.  It can either be simply placed at ‘ground level’ or if needed ‘raised’ using uprights.

First it’s a good idea to use pegs and string to set out the deck perimeter.  Clear all turf and vegetation and firm the ground if needed.  It’s a really good idea to lay weed inhibiting membrane down on the area at this point to stop any nasties coming through.

Decking Frame

The framework should be put on concrete foundations.  You could lay concrete for this but slabs are a lot easier.  Slabs would normally be placed in a grid pattern about 1400mm apart to allow for adequate support for the joists.  If you have bad drainage or poor soil condition consider using poured concrete in holes of at least 300mm square.  Use a spirit level and try to make sure the deck slopes (away from the house) roughly 10mm for every meter.

Create the outer frame of the deck with pressure treated, tanalised timber.  150mm x 50mm is ideal.  Where the timber touches the ground use a damp proof course membrane.  In our ‘ground level’ method these joists will simply be placed on the ground being supported by the concrete grid.  For the ‘raised’ method these will be supported by uprights, I recommend 90 – 100mm sq tanalised timber.

With the frame in place use at least 100mm screws and wood glue to fix it together.  If the decking is being attached to the house make sure you add plenty of spacers to allow for a drainage gap.  Stainless steel washers are excellent for this.  Next you will infill the outer frame with joists spaced at 400mm intervals.  These should be at right angles to the finished decking tiles or boards.  You could use off cuts of timber to create noggins in between the joists for extra strength.

Laying the Decking

Once your framework is complete and totally rigid you can start laying your decking boards or tiles.  Lay about 6 boards at a time, I have already mentioned an expansion gap and to accomplish this evenly I tend to use a decking screw as a spacer (remove after fixing).

A few notes on fixing your decking boards:

  • Always use stainless steel or galvanised screws, there’s nothing worse than seeing rusty screw heads and stained decking boards.
  • Always pre-drill your screw holes, without this you run a risk of splitting the timber.
  • Screw the end of the boards first and then to every joist.
  • If the decking boards are wider than the deck you must make sure you stagger the boards and that joints are over a joist.

Raised Decks

Raised decks are slightly trickier and need a little bit more thought.  As I mentioned you will be using uprights of about 100mm square.  These will be held in place using metal supports of either a bolt in style or an adjustable concreted anchor.

Bolt down post anchors

Bolt down post anchors

 

Concrete anchor for posts

Concrete anchor for posts

 

The frame is constructed as above but will be utilising joist hangers for added strength.

If the deck is over 60cm in height we strongly recommend a rail to prevent a nasty fall.

Also, any cut timber or drill holes would benefit from a timber treatment

I hope this has been helpful.  If you need any help or advice with your decking project please contact us