Construction questions, floor joists in extension

tlundberg · 13 Jul 2015 at 6:15 PM

I have a foundation wall according to the picture

Concrete foundation wall corner with layered blocks, shown without external insulation or additional structure, for a construction project discussion.

On the outside, I have placed 20 cm thick isodrän below ground and above ground there will also be 20 cm of insulation

Foundation wall with red base and white insulation layer, showing L-shaped corner, prepared for floor joist construction and further building.

On top of that will be the actual extension, with the facade panel a few centimeters outside the insulation on the foundation wall

3D model of a building structure with a red facade, brown foundation, and gray roof, showing layers of foundation and insulation setup.

But I haven't quite gotten that far yet... I'm having trouble figuring out how to construct the floor joists. First, I place a sill plate on the wall, and then I place the floor joists on the sill plate

Illustration showing a foundation wall with wooden floor joists placed on top, highlighting construction elements for an extension project.

But what do I do with the outermost floor joist? It doesn't have a foundation wall/sill plate to rest on

Building diagram showing foundation wall with wooden beams on top. The red layer represents insulation. Image illustrates floor joist placement issues.

Does anyone have a smart solution proposal?

tlundberg · 13 Jul 2015 at 6:22 PM

Is it enough with noggins at cc 60? The entire outer wall will be out there and weigh down...

A wooden floor framework with joists and noggins, discussing the adequacy of joists at 60 cm centers to support an outer wall load.

leby · 13 Jul 2015 at 6:35 PM

You should not have the beam layer outside the wall. I assume you thought of that to get outside the insulation, but it is wrong according to what I have learned.

tlundberg · 13 Jul 2015 at 6:37 PM

Yes, exactly, it's to get outside the isolation on the foundation wall. How should I do otherwise?

leby · 13 Jul 2015 at 6:43 PM

The insulation inside the wall, there is stone with built-in insulation. Below ground you can have isodrän.

tlundberg · 13 Jul 2015 at 6:47 PM

It's too late, the wall is already built

Pagno · 13 Jul 2015 at 6:49 PM

You should probably move the joist into the correct position, above the wall, that is! From a construction-technical standpoint, it is not advisable to tinker with special solutions. The point of the wall is that there should be a frame around the entire joist, from which you then start when you "cover" over the insulation on the wall. So, nothing protruding outside the wall when it comes to the ground joist in your case. Otherwise, there are joists in other materials such as steel constructions, concrete joists of various designs.

Gabbe1 · 13 Jul 2015 at 7:27 PM

If you build with standing studs, for example, 120x45 (which stand on the lecamuren), you can then cross-brace externally with 95x45. This will provide space for 100mm cellplast/isodrän outside the lecamuren.

Pagno · 13 Jul 2015 at 7:45 PM

The problem is that ts wants 20 cm......

tlundberg · 13 Jul 2015 at 7:46 PM

I have already installed 200 mm isodrän, and I plan to install the same thickness of cell plastic.

Can I cross-batten with an additional 95 mm on top of the cross-battening you suggest?

Gabbe1 · 13 Jul 2015 at 8:13 PM

Everything is possible, but then it starts to be quite a lot of weight that burdens the screws in the first cross brace.

Must the house's facade and foundation line up exactly?
Perhaps one could have a drip cap at the bottom that extends over the foundation's insulation?

tlundberg · 13 Jul 2015 at 8:36 PM

Yes, it will be quite heavy. I wonder if it wouldn't hold better the way I sketched it...

As mentioned, it's an extension and I want it to look the same here as it does on the existing part of the house (there's a different foundation type there, without insulation). Therefore, I'd prefer to avoid drip edges.

leby · 14 Jul 2015 at 8:56 AM

I still don't believe in your solution. The loads are completely wrong. If you're already standing here, I would try some form of steel construction. Otherwise, if you want to be very inventive, do as you have drawn but place the wall inside the wall, say you place a 145x45 furthest in to be the support, then build as Gabbe suggests on the outside, then the wall carries the wall and your insulation studs are carried by the floor joist extension. Not exactly a normal construction. Of course, the best thing is to talk to a structural engineer.

tlundberg · 14 Jul 2015 at 9:07 AM

I hear what you're saying, but I'm still not going to give up without further discussion

It's only on the long side, with the floor joist hanging in the air, that there's a problem with my solution, we agree on that, right? On the short sides, there can't be any problems, can there?

leby · 14 Jul 2015 at 10:21 AM

It is primarily on that side that you placed noggings, not really good on the other side either but it will probably hold anyway. How much insulation were you planning? Today the building standard is standing 195x45 and lying 45x45, I believe. Since you're using insulation in the basement section, maybe you've planned the same for the wood construction? Place a 195x45 at least 95 on the wall and then lay a 95x45 outside. It won't be great, but it will probably hold.