Thermal Bridge across RSJ?

[iDIY]

Hi guys,

As shown in the attached picture, I am building a 2 story building, garage below, art studio above. The garage is not subject to regs but the studio is.

The design has an RSJ supporting the full upvc frontage.

given the RSJ is exposed on the outside, it is supported on the inner leaf and it’s supporting the inner and out relief walls, surely that is a significant thermal bridge and as such against regs?

 

[Leofric]

If you are building a new 2 storey building comprising a studio over a garage don't you get it all approved under building regulations
Yes, a steel beam supporting the inner and outer leaves of an external wall is a cold bridge ,you need to minimise the risk of condensation due to cold bridging by thermal insulation (a construction detail drawing required ) I would have 'proper' architectural drawings prepared for the whole building so that it complies with building regulations.

 

[iDIY]

If you are building a new 2 storey building comprising a studio over a garage don't you get it all approved under building regulations

No, the foundations had to be and were inspected by BCO but the garage is still a garage and as such does not have any thermal requirements under regs. As such the garage walls are effectively just part of the foundations holding the upper level in place..

 

[Leofric]

No, the foundations had to be and were inspected by BCO but the garage is still a garage and as such does not have any thermal requirements under regs. As such the garage walls are effectively just part of the foundations holding the upper level in place..

Not thermal insulation but the walls are structural . The walls aren't really part of the foundations ,the walls are built off the foundations and support the studio above so need to be considered under bldg. regs. The studio floor needs to be insulated of course.

 

[iDIY]

Not thermal insulation but the walls are structural . The walls aren't really part of the foundations ,the walls are built off the foundations and support the studio above so need to be considered under bldg. regs. The studio floor needs to be insulated of course.

well obviously, but as I said, not for insulation which is what this thread is about.

 

[Leofric]

As long as you know what you are doing.​

 

[Notch7]

well obviously, but as I said, not for insulation which is what this thread is about.

I would imagine your art studio will need to comply with part L.

A steel beam either needs to be all on the warm side, or it will need a thermal break -ie clad in PIR celetex.

Im not sure if it needs fire protection as well?

 

[^woody^]

Theoretical thermal bridges are not the same are actual thermal bridges.

 

[iDIY]

I would imagine your art studio will need to comply with part L.

A steel beam either needs to be all on the warm side, or it will need a thermal break -ie clad in PIR celetex.

Im not sure if it needs fire protection as well?

it will need fire protection where it’s exposed in the garage as I understand it. For insulation I’m thinking pir on the vertical faces of the RSJ between the timber joists. Then a upvc facia piece to provide mechanical and weather protection to the pir.

 

[iDIY]

Theoretical thermal bridges are not the same are actual thermal bridges.

is that a theoretical solution

 

[^woody^]

... actual solution

 

[iDIY]

I’m thinking along these lines re thermal insulation?

 

[John D v2.0]

Thermal bridges are mainly problematic because of condensation. The humidity in a garden studio would usually be lower than in a kitchen, which is where these kind of beams are usually found.
So you are likely to get away with more than the worst case, which the regs and calculations assume. I presume that's what woody is getting at when he differentiates the worst case theory with the actual situation.
Having said all that on our kitchen beam the outside was clad with a thin layer i think 25mm of polystyrene insulation before the render went on, and there hasn't been any obvious condensation yet.
uPVC fascia board isn't really insulation, and there's a lot of surface area of steel on the cold side there.

 

[iDIY]

Thermal bridges are mainly problematic because of condensation. The humidity in a garden studio would usually be lower than in a kitchen, which is where these kind of beams are usually found.
So you are likely to get away with more than the worst case, which the regs and calculations assume. I presume that's what woody is getting at when he differentiates the worst case theory with the actual situation.
Having said all that on our kitchen beam the outside was clad with a thin layer i think 25mm of polystyrene insulation before the render went on, and there hasn't been any obvious condensation yet.
uPVC fascia board isn't really insulation, and there's a lot of surface area of steel on the cold side there.

thanks John that makes sense. The fascia is proposed to provide protection to the PIR insulation.

 

[Leofric]

That sketch does not insulate the flange where the cold bridge occurs. Looks a tricky detail at the interface of wall/floor/decking - needs a proper construction detail drawing. Looks as though there might be some other 'interesting' construction details on that job.