Insulating Steels in House extension

[Ay8452]

Hi guys, 

 

I am doing a renovation and extension of a 1930s house. The extension has a fair amount of steel work and am looking how to sensibly/practically insulate this. What are the recommendations for insulting steel beams and columns? I'll post a couple of scenarios I have below. 

 

1. SCENARIO 1: If the internal web of the steel beam has floor joists etc and the external web is empty/bridging the thermal envelope then pack PIR insulation in the external web/foam and then finish with render board so flush silicone render finish externally. Should I leave a space between the PIR and the renderboard externally to stop moisture ingress? Should I be adding a VCL somewhere internally to this steel? I was considering adding aerogyl strips to the internal aspect of the web (10mm thick) to reduce cold bridging - should this have a VCL added to it?
2. SCENARIO 2: If the internal web of a steel beam is empty and the external web has joists (e.g. flat roof joists for cold flat roof detail) then pack PIR insulation in the internal web and all warm side surfaces of the steel and foil tape it so stop moisture getting to the steelwork.
3. SCENARIO 3: If the internal and external web of a steel beam is empty then pack PIR insulation in the internal web and all  warm side surfaces of the steel in the internal web and foil tape it so stop moisture getting to the steelwork. Should I also pack PIR insulation into the external web as well?

 

Have a few other scenarios but will try work those out based on answers for above. Thanks!

 

[Mike]

If the outer leaf of the house is non load bearing, then another option could be to confine the steelwork to below the inner leaf, then use Ancon brickwork supports (or similar), which can be fitted with thermal breaks, to support the outer leaf.

 

[JohnMo]

Each one of your options is not really insulated at all. The horizontal webs have to insulated from the outside world. The PIR is really doing nothing to help you.

 

Draw lines start at one piece of insulation and if there any gaps in your line, you have a thermal bridge to fix.

[ETC]

Use two beams.

[Russell griffiths]

This ⬆️

[Ay8452]

2 hours ago, JohnMo said:

Each one of your options is not really insulated at all. The horizontal webs have to insulated from the outside world. The PIR is really doing nothing to help you.

 

Draw lines start at one piece of insulation and if there any gaps in your line, you have a thermal bridge to fix.

 

Thanks all for comments. Too late to use two beams unfortunately. If I use aerogel strips and overlap them on the warm side and overlap them either side of the cold bridge area - will that not resolve the cold bridge? I can also apply aerogel externally (cold side) and do the same + plus pack the web with PIR ? Try to make the best of the current situation.

[JohnMo]

If you draw out, what you mean, that would be great.

 

The wood and PIR packing is just acting as packing, doing very little insulation. Your yellow beam horizontal parts will be the same temperature as outside and they are bypassing all insulation.