Hello
I'm planning to build a sunroom on the south wall of an old cottage with a crawl space foundation.
I have two questions before I intend to start.
I found a good construction description on Finja's website where they used Sulformsblock. That seems convenient, but is it necessary? Can I dig and lay concrete blocks directly on gravel about 40cm down? That would make it two layers of concrete blocks below ground, and then I'm thinking about two layers above ground. The rest will be framed.
How do you attach it to the house? I think I can attach a wall stud to the panel. But the concrete blocks, you don't want them directly against the panel, right? Against the stone foundation, I'm thinking of sealing with mortar.
See the pictures as a work in progress. The posts are 90x90, the sill is 45x120. The windows are the only fixed limitation I have. They are already purchased (used).
I'm planning to build a sunroom on the south wall of an old cottage with a crawl space foundation.
I have two questions before I intend to start.
I found a good construction description on Finja's website where they used Sulformsblock. That seems convenient, but is it necessary? Can I dig and lay concrete blocks directly on gravel about 40cm down? That would make it two layers of concrete blocks below ground, and then I'm thinking about two layers above ground. The rest will be framed.
How do you attach it to the house? I think I can attach a wall stud to the panel. But the concrete blocks, you don't want them directly against the panel, right? Against the stone foundation, I'm thinking of sealing with mortar.
See the pictures as a work in progress. The posts are 90x90, the sill is 45x120. The windows are the only fixed limitation I have. They are already purchased (used).
Tool enthusiast
· Stockholm
· 101 posts
Maybe a bit late reply...
The sulforms blocks are a convenient way to achieve a large base area against the ground, as well as allowing space for extra reinforcement on the top of the blocks, in the depression. When you fill with concrete and cast the reinforcement, the blocks can take quite a large compressive load. It becomes like a concrete beam on the top. If you have a heavy masonry wall on top of the bottom layer of blocks, and the ground is soft, the bottom block layer can sink unevenly into the underlying ground, causing a settlement and a possible twisting between each block. (A complexity with LECA walls compared to wooden walls is that LECA walls are quite heavy, thus exerting significant pressure on the ground beneath). The displacement can then propagate as settlement through the whole masonry, resulting in cracks. In the worst case, you may observe visible tilts in the wall. This is counteracted by a reinforced concrete beam at the base of the wall, making the wall as a whole less sensitive to local ground movements.
It is very difficult to generally state what suffices, as it depends on ground conditions. Construction instructions for LECA walls usually suggest that the wall is built on a properly steel-reinforced concrete beam that is cast on-site, or that you use such sulforms blocks to avoid having to build a wooden form for the casting work.
In your case, the wall is quite low, so the weight is somewhat less than a full LECA wall, meaning lower requirements for the strength of the lower layer. Have the blocks been placed on well-compacted gravel? What is the base, what type of soil? If you have frost-heaving soil or clay, you should remove that soil and replace it with gravel all the way down to frost-free depth, which can be a demanding project in itself. Additionally, you have the problem of digging too close to the existing house foundation, which may also experience settlement if you have to dig down 1-2m right next to it. Here, one must weigh how ambitious one can be, is it worth the foundation work costing 3 times more than what is visible above ground just to avoid seeing a small crack in the LECA wall in 20 years?
There are also other alternatives, as mentioned, to using sulforms blocks. A site-cast concrete wall is perhaps the closest alternative. The problem is that it will require large amounts of concrete, 100 times more than to fill the sulforms blocks. It can be demanding to mix these quantities of concrete in a mixer. Ready-mixed concrete is recommended.
Another option is to lay out 19x29x59 blocks sideways, upside down, so that they span 59 cm across the wall's length direction, thus providing a larger base area against the ground and the smooth LECA surface facing upwards. Then you can build a wooden form on top in the middle of the blocks and reinforce, a low concrete slab about 15 cm high and the same width as your LECA blocks with which you will build the rest of the wall. On top of the concrete slab, you can then construct the LECA wall.
The sulforms blocks are a convenient way to achieve a large base area against the ground, as well as allowing space for extra reinforcement on the top of the blocks, in the depression. When you fill with concrete and cast the reinforcement, the blocks can take quite a large compressive load. It becomes like a concrete beam on the top. If you have a heavy masonry wall on top of the bottom layer of blocks, and the ground is soft, the bottom block layer can sink unevenly into the underlying ground, causing a settlement and a possible twisting between each block. (A complexity with LECA walls compared to wooden walls is that LECA walls are quite heavy, thus exerting significant pressure on the ground beneath). The displacement can then propagate as settlement through the whole masonry, resulting in cracks. In the worst case, you may observe visible tilts in the wall. This is counteracted by a reinforced concrete beam at the base of the wall, making the wall as a whole less sensitive to local ground movements.
It is very difficult to generally state what suffices, as it depends on ground conditions. Construction instructions for LECA walls usually suggest that the wall is built on a properly steel-reinforced concrete beam that is cast on-site, or that you use such sulforms blocks to avoid having to build a wooden form for the casting work.
In your case, the wall is quite low, so the weight is somewhat less than a full LECA wall, meaning lower requirements for the strength of the lower layer. Have the blocks been placed on well-compacted gravel? What is the base, what type of soil? If you have frost-heaving soil or clay, you should remove that soil and replace it with gravel all the way down to frost-free depth, which can be a demanding project in itself. Additionally, you have the problem of digging too close to the existing house foundation, which may also experience settlement if you have to dig down 1-2m right next to it. Here, one must weigh how ambitious one can be, is it worth the foundation work costing 3 times more than what is visible above ground just to avoid seeing a small crack in the LECA wall in 20 years?
There are also other alternatives, as mentioned, to using sulforms blocks. A site-cast concrete wall is perhaps the closest alternative. The problem is that it will require large amounts of concrete, 100 times more than to fill the sulforms blocks. It can be demanding to mix these quantities of concrete in a mixer. Ready-mixed concrete is recommended.
Another option is to lay out 19x29x59 blocks sideways, upside down, so that they span 59 cm across the wall's length direction, thus providing a larger base area against the ground and the smooth LECA surface facing upwards. Then you can build a wooden form on top in the middle of the blocks and reinforce, a low concrete slab about 15 cm high and the same width as your LECA blocks with which you will build the rest of the wall. On top of the concrete slab, you can then construct the LECA wall.