Bases – Everything You Need to Know
Over the many years we have been in business, we have had numerous clients come to us, and ask us about what types of bases would be suitable to support the log cabins, and also our builders have turned up to jobs and encountered many bases which are far from suitable to build off.
This page gives a brief overview on different types of base systems, and what to look out for.
Concrete slab
This is by far the most common, and the most suitable type of base to build a log cabin on top of. Generally speaking, the spec of the base does not need to be anything overly engineered and we generally find that 100mm thickness to 150mm thickness of slab would be sufficient assuming good ground.
It is important however that the base is level and we ask for a tolerance of +/- 5mm to work to, to give a suitable level hardstanding for the cabin to sit on.
We would advise that the slab is not flush with the existing ground level, as you could encounter surface drainage issues. So we would always ask that the slab is at least 50mm above highest ground level.
For our clients who purchase through us, we would send out a PDF document with your order detailing the spec of how a concrete slab should be laid.
Raised timber base
We can supply and install a raised timber base for your log cabin. This solution is ideal for sloping/undulating ground, or perhaps where site conditions make it very difficult to pour a concrete slab, or an alternative option where a concrete slab is not wanted.
We first create a gridwork of concrete padstones, roughly 300 mm x 300 mm x 300 mm at no more than 2000 mm pitch. On top of each concrete padstone we use 150 mm x 150 mm HDPE spacers and then sit large 150 mm x 150 mm pressure treated timber legs on top.
We use the HDPE spacers so that the timber legs are not sat in any surface standing water.
The 150 mm x 150 mm timber legs are cut to length, so that the top of each of the legs are level with one another.
From each timber leg we span large 200 mm x 75 mm timbers around the perimeter and across each run to create ‘grids’.
Within each grid, we span 150 mm x 50 mm timbers, in the opposite direction at no more than 610mm pitch.
On cabins with an insulated floor, we then overlay the whole lot with 11mm OSB, in order to support the damp proof membrane and the floor insulation boards.
The cabin walls then sit on 58 mm x 58 mm pressure treated bearers, and we use the same section size of timber for the floor joists. These joists will run in the opposite directions to the 150 mm x 50 mm timbers, thus being supported at 610mm intervals, which gives adequate strength.
The finished cabin sat on top of the timber base would look like the photo below.
This type of system is tried and tested, and something which we have been creating for our clients over the past 22 years we have been in business.
It is an extremely versatile system meaning we can deal with highly significant ground slopes.
Ground screws & Easy Pads – everything you need to know
Increasingly so, we are being asked more and more by clients/potential clients on what are our thoughts on base systems like ground screws or Easy Pads.
This section is to detail the additional requirements for the foundation which may not be obvious when starting to look at these potential foundation systems.
Generally speaking, when you are looking to purchase a log cabin from us, the cabin and the flooring is designed for sitting on a concrete slab. As soon as you elevate it from the ground using one of these systems, then the standard flooring is no longer suitable to work with such systems.
The standard cabins are supplied with 58 mm x 58 mm pressure treated sole plate and floor joists. The sole plate runs continuously under all the external walls (and partition walls if you have them), and they are used to support the flooring, with joists positioned at a pitch of 500 mm.
A timber of this size (58 mm x 58mm) cannot span any greater than 610 mm unsupported!
If we take a relatively basic cabin size of say 4m x 4m with 58mm sole plate and bearers. Across the front 4m dimensions you would need 8 ground screws or easy pads to ensure you do not exceed the maximum unsupported distance. This is the same for the floor joists, so effectively you would need a gridwork of 8 No. x 9 No. = 72 No. ground screws/easy pads to support the cabin effectively. This of course, is a ridiculous and expensive quantity, and if you have a floor insulation system, which sits between the floor joists, how is this supported? It is not, so simply falls to the ground and becomes useless.
So, the way to achieve a much more modest quantity of ground screws/easy pads, and to ensure you have a solution for supporting the floor insulation is to build a substructure which can span much greater distances thus reducing the quantity of supports beneath it.
The substructure which would be required would essentially be identical to the structure of the timber base described in the above section. By creating this type of substructure you would then limit the amount of ground screws/easy pads to 9 (assuming adequate load carrying capacity of the supports) for the same sized log cabin.
Again, similarly with the above raised timber base system, if the cabin includes a floor insulation system, then the substructure would be overlaid with the same 11mm OSB to support damp proof membrane and insulation boards.
What is important though is if you did something like this, the cabin floor height above the highest ground will be significantly taller i.e. minimum height of ground screw/easy pad above highest ground (suppliers to detail this) + 200 mm thickness subframe + 11mm OSB = 211 mm + 58 mm cabin joists + 19 mm tongue and groove floor = 288 mm minimum above the ground screw/easy pad.
If you chose to go down the route of ground screws/easy pads, we would need to know this information prior to you ordering so that we can design the floor correctly, and issue you with a design for the substructure which you would need to create.
What we cannot do, is advise on the suitability of such supports, and what weights/loads they can carry.
This is for the supplier of such systems.
Raised timber base v ground screws/Easy Pads
Cost
The cost of the 150 mm x 150 mm timber legs, HDPE spacers, and small amount of concrete required, are significantly more cost effective than a ground screw or an Easy pad. Both require the same sub structure above them, so the only cost comparison is between the legs required, where the timber legs will always win.
Ground slope
As detailed above there is much more versatility with the raised timber base over the ground screws/easy pads. Easy pads have a max adjustment of 150mm. Ground screws whilst there are different lengths available, it becomes quite tricky and highly expensive being able to deal with significant ground slopes.
Environmentally friendly
There is minimal concrete required for a raised timber base, and should the building/foundation require removing from the site, breaking up a small concrete padstone and removing it is a pretty simple task. Easy pads still use concrete, and they still require ground excavation and is still recommended that hardcore is used. So one, is no more environmentally friendly than the other.
Convenience
The biggest pro for choosing the raised timber base, is that we can do the design for it, and we can supply all materials, and carry out the installation of it.
It makes commercial and logical sense if you are looking for a more environmentally suitable option for your base for the cabin, or an option for undulating/sloping ground.
Patio
Is a patio suitable enough to build on? The general answer to this is ‘maybe’.
Commonly if you already have an existing patio, where you wish to build a cabin on top of it, there is a good chance that the patio would have been laid with a drainage fall on it, so that you do not have a puddling issue. This of course is not suitable for building on top of.
So if you do have an existing patio, please check the levels of the patio first before deciding whether it is suitable. If there is a slope across the patio, please advise us on how much slope there is and over what distance so that we can calculate whether we think this will be suitable, or whether anything would need to be done prior to the cabin’s arrival.
If your intention is to lay a patio ready for the cabin, then this may be absolutely fine. However, it is important that you lay the patio so each slab is level with one another and level overall working to the same tolerance of a concrete base i.e. +/- 5mm.
The patio slabs would still need to be laid suitably i.e. dig off the area you intend to lay the patio by a reasonable depth (150mm), fill with compacted hardcore, followed by a thin layer of concrete mix say around 50mm, and then the patio slabs on top of this.
Just throwing some patio slabs onto the ground will not be strong enough to support the weight of the cabin.
Decking
Will a decking be suitable to build on top of? Again, the answer is ‘maybe’.
If you already have a decked area either a wooden decked area or a composite decking area and would like to know whether it would be suitable to build on top of. The important question is, what is the decking built on top of? i.e. what is the subframe and how was the subframe constructed?
If the answer to this is unknown, we cannot say that yes it would be suitable, and likely we would not wish for our builders to build on top of it for safety reasons.
If you do know exactly how the substructure was constructed, then we would like to know this information to be able to appraise whether it would be suitable to build on top of it.
Again it is important that the decked area is level within the same tolerances of +/- 5mm.
If the intention is to create your own decked area prior to the cabin’s arrival, we would like to be consulted on the way in which the substructure is constructed so we can appraise its structural integrity to support the weight of the cabin.
