However, when talking of wooden houses (and A-frame are generally wooden houses) there is an aspect of the foundation that becomes particularly important.
...and no, it has nothing to do with strength...
We'll come to that ONE detail in a moment, but first, let's see which is the best type of foundation for an A-frame house.
The best foundation for an A-frame house
The base the A-frame (bottom part of the triangle) works as an insulated floor slab (at least in Avrame models) and this means this kind of construction does not need to rest on a flat foundation slab.
In fact, it is recommended to leave at least 30cm/ one foot of clear space between the bottom of the floor construction and the ground.
For this reason, a flat concrete slab (very common with wooden element houses) is NOT the ideal type of foundation for an A-frame house.
This turns out to be a good thing since flat concrete slabs require a lot of concrete (plus a lot of excavation work), so they are very expensive to make.
The base of the A-frame is strong and self-supporting, therefore it needs only a few points of connection to stand safely.
Solo and Duo houses can stand on 3 points.
Given the longer span of the base, Trio houses need to be supported on 5 points.
The best type of foundation to provide this kind of support is the strip foundation.
As an alternative (and depending on the ground), a pile or pile-and-beam foundation can be used.
The benefits of the strip foundation
Compared to a flat concrete slab foundation, there are several evident advantages when using a strip foundation.
Here is a list of the most compelling:
- Less excavation works.
Since the footprint of the strips is way smaller than the total area of the floor, excavation is localized and the total volume of soil to be moved is greatly reduced.
- Less concrete and steel.
The strips are geometrically smaller than a full-size slab, therefore way less concrete is needed in the casting process.
Also, reinforcing steel bars are needed in a smaller amount.
- Less insulation material and works.
People tend to forget that foundations have to be insulated to the same level of other house components (walls, roof).
Since in Avrame house the insulation is contained in the base of the A-frame, the foundation strips do not need to be insulated at all.
This makes the foundation works way easier, cheaper, faster.
- Less time.
As a result of the three points above, strip foundations can be built in a fraction of the time of flat slabs.
Pile foundations share the same benefits, although they generally need deeper digging that can result in more expensive excavation works.
The most common mistake
Let's come to the juicy part: the mistake that will cost you money.
This mistake is something we find pretty often.
For a while, it left us scratching our heads...
Why do builders keep making this dumb error?
This is the error: the foundation built on the site is slightly different from the one described in the design documents.
- strips are not leveled
- the surface of the strips is not uniform
- strips are not aligned
What is the consequence?
In order to be installed correctly, prefabricated wooden constructions - be it pre-cut or elements or modular - need a perfectly leveled foundation.
The direct consequence of the mismatching between building and design is that the foundation has to be fixed before the A-frames can be installed.
This results in additional labor, materials, time (and money of course).
In some cases, part of the newly built foundation has to be demolished to allow for corrections.
You can imagine the frustration and bad mood of the owner when this stuff happens...
Why this mistake?
Really, we've been thinking a lot about what could be the reason builders do not execute the works as instructed. Then it struck us...
In traditional brick & mortar buildings, having a perfectly leveled foundation is NOT a requirement. This is because every imperfection can be fixed when laying the bricks. Even a mismatch of several centimeters can be recovered within the first few rows of bricks.
So here it is:
builders who are used to build with bricks do not understand the importance of having a perfectly leveled foundation, therefore they do not strive to get one.
Of course, they can see the drawings and they are fully aware the foundation is not a 100% match... but they do not see the problem.
They are used to fix that in later stages.
Mindblowing... isn't it?
How to avoid it
The obvious way to avoid this problem is to give the work to a crew with experience in prefabricated wooden buildings.
Depending on the location, this might not be easy or feasible at all.
If you are forced to work with a crew of traditional builders, you have to explain the importance of having a perfectly leveled foundation.
Here are two tips on how to go about it:
- address this topic from the beginning.
Get a first price offer for the foundation works. Then explain the need for perfectly leveled foundation and expect the builders to ask more money to accommodate that request.
If they do, they understand the extra effort they have to make.
If they say "no problem" and they don't ask you for more money... then you should be concerned and stress it once more... then you move to the next point.
- be very clear that any eventual fix of the foundation shall be done by the builders free of charge.
Seriously, have this written in your agreement with the builders... so they'll understand how important this point is to you.
This foundation thing is a very subtle issue that no one will tell you.
Sadly, it is one of those issues that will hit on your budget and your nerves.
If you are going to build your own home, you need to put yourself in the position of not making this kind of mistakes.
We are here to help.
Our 100 Questions Guide was developed especially for this: to put you into the right mindset and to set you on a mistake-free course.
Even if you don't get the guide, just know there are so many things that could go wrong when building your house on your own... so you need to do your homework and get some knowledge before you take action.