how to frame up a new (and sturdier) floor on concrete joists?

[Enber]

I am planning to install underfloor heating in my 1960s townhouse with concrete slab floors of the type ERGE/SCG, which consist of concrete beams spaced at CC 120 and thin concrete elements in between resting on the lower flange of the concrete beams. On top of these currently lie 70x45 joists with a nailed board (about 22-23mm thick) as a subfloor (see sketch). There is some flexing, but I don't have room to increase the building height any more than it is.

I'm considering the following solution: I place 95x45 joists, which I saw 25mm out of where they rest on the concrete beams (so that 70mm remains there). Then I screw-glue the underfloor heating panels to increase the stiffness further. Do you think this could work sufficiently well? I can't find any sizing tables that describe 95x45, but I feel reassured that 120x45 is said to clear over 2 meters according to the timber guide.

https://www.traguiden.se/konstrukti...uktionsvirke-i-ett-fack/?previousState=001000

(Edit: Aiming for cc 600 for the new floor joists)

 

[Tompafix]

I will install underfloor heating in my 60s terraced house with ERGE/SCG type concrete slab, which consists of concrete beams at CC 120 and thin concrete elements in between resting on the lower flange of the concrete beams. On top of these are currently 70x45 battens with a nailed board (about 22-23mm thick) as a subfloor (see sketch). This has some give, but I have no space to increase the building height more than it is today.

I'm considering if the following solution could work?: I lay 95x45 battens that I saw 25mm into in the places where they rest on the concrete beams (so that 70mm remains there). Then I screw the underfloor heating channels to increase stiffness more. Do you think this could work well enough? I can't find any sizing tables that describe 95x45, but I find it reassuring that 120x45 is stated to handle just over 2 meters according to the wood guide

[link]

(Edit: Aiming for cc 600 for the new floor joists)

Seems like a big job to notch every single batten...
A 70 batten should handle about 1.2m at cc60.
If you reduce to cc30, they handle about 20% more. About 1.3m. Additionally, if you screw-glue, the load capacity increases by about 30% more compared to nailed as you can see in the table.

 

[Enber]

Thanks Tompa!

I'll take the tip about making it easier for myself, it will probably be reasonably strong anyway. What still makes me a bit unsure is that I can't find any construction-graded timber C24 in the dimension 70x45. Maybe simpler qualities will still work?

Otherwise, I think a small plunge saw would make the job of notching easier, but you're right that it will be quite a bit of work .

 

[Tompafix]

You could make a test plate and lay it over the concrete supports to test it.
Then maybe another way to reinforce the whole thing is to add kortlingarna between all the beams. Like halfway between the concrete supports.

 

[nino]

You can't just buy spikvinklar, which you attach to the concrete and align the stud and screw it into place, then you can set cc300 if you want and avoid tearing everything down.

 

[Tompafix]

Thanks Tompa!

I will take the tip about making it simpler for me, it might still be reasonably strong. What still makes me a bit unsure is that I can't find any construction-rated wood C24 in the dimension 70x45. Maybe it still works with simpler qualities?

Otherwise, I think a small plunge saw makes the job of notching easier, but you're right that it will be quite a bit of work .

C24 45x70 is not available everywhere. But a quick search found some anyway. You should search the stores you have nearby.

 

[Enber]

Just to follow up, I eventually went with 95 beams and notched with a small plunge saw. It took quite a bit of time, but after a few beams, I picked up the pace and feel that the floor is stable now at least.

Thanks for all the help!

 

[Tompafix]

Fun to hear 👍What cc measurement did you end up using?

 

[Enber]

It ended up being about cc60 between the 95 studs, I have turntables for LK underfloor heating at the ends (which are about 60), then I adjusted the distance in between to make it a bit comfortable, just under cc 60 (LK's straight floor chipboards do not need to have the studs at a specific measurement as long as it is under 60 since joints don't need to be on a stud).