rsj - preventing thermal bridge

[John D v2.0]

We are building a single floor extension with a 4.8m opening. The SE has designed a 152 uc.

How do people normally resolve the thermal bridging?

For background At the moment it's welded to a 300mm wide full length plate which is sitting on concrete pad stones that bridge the cavity.

The architect is suggesting we clad the whole rear wall with 30mm of some vacuum insulation that is a special order. It's 3 times as insulating as normal celotex. I need to get this sorted with the builder.

Any help would be very gratefully received!

 

[tomfe]

Is this opening in the new extension or the original house?
Your 'architect' is having a laugh at vacuum insulation.

 

[cjard]

It's ten times the price of normal celotex too!

Really need to see the detail on some plans, then we can work out what you're actually trying to insulate and how external facing it is.

 

[John D v2.0]

Thanks very much for the quick replies, I really appreciate it!

Is this opening in the new extension or the original house?
Your 'architect' is having a laugh at vacuum insulation.

It's in the new extension. At present the walls are up to padstone level and the beams are sitting on top. And yes I wasn't quite sure how to respond to his suggestion.

It's ten times the price of normal celotex too!

Really need to see the detail on some plans, then we can work out what you're actually trying to insulate and how external facing it is.

You're getting mixed up with aerogel. This is even "better" insulation than that. Unless you're trying to get hold of some.For a good price.... It's this one he's suggesting http://www.kingspaninsulation.co.uk/Products/OPTIM-R/OPTIM-R-External-Wall-System/overview.aspx

Here is a section through the beam as drawn (the one on the right), although the beam fitted is incorrect in that it has a extra wide bottom flange. You can see the insulation on the outside of the parapet it should supposedly cover the whole external wall and into the reveal.

Another useful point is that we haven't yet ordered the doors, so we can reduce the size of them no problem to fit insulation.

 

[tomfe]

So you are going with a solid wall, why not put ewi on? 100/150mm of graphite eps. You have kind of mitigated the thermal bridge with your iwi in the roof.

 

[John D v2.0]

So you are going with a solid wall, why not put ewi on? 100/150mm of graphite eps. You have kind of mitigated the thermal bridge with your iwi in the roof.

Hi Tom thanks for replying again, that's helpful. Would you continue the graphite eps around into the top reveal and make the window frame 100mm smaller? To stop the heat conducting through the steel from inside to outside. If that, I'm not sure how to hang the window.

 

[tomfe]

Sorry I had presumed you where doing a solid wall build and not just solid wall above your uc.
What is your full make up of the wall?

I'd used 2 90mm shs one for inner and one for the outer leaf but it's too late now

 

[John D v2.0]

Hi Tom that's ok. The walls at the sides are 100mm concrete block, 50mm celotex, 50mm space, 100mm block.

See the attached sketch of the beam as fitted currently. I drew a kind of perpective view as well as the section to make it more clear hopefully.

Inside is the left hand side in both.

I see SHS is a square hollow section, I can always ask the SE to calculate for that and just pay for a replacement. But wouldn't they "fall off" the wall without some serious tying together? And I don't think I need a lintel on both leaves as the inside one doesn't actually need anything built over it.

 

[^woody^]

Why hasn't the Architect specified a properly detailed solution without a thermal bridge, and why hasn't the SE taken this into account with his design?

You've got two numpties there without a clue between them.

 

[tomfe]

You could push the uc to the inner leaf and then insulate up to your parapet.

 

[John D v2.0]

Good idea Tom, so more like this? (standard detail from the window supplier)

 

[tony1851]

Whatever happened to a timber beam on the inside, and using the window frame on the outside?
At least that's how we did it when I started out.

 

[tomfe]

(standard detail from the window supplier)

If you need to extend the fixings out from the uc you can use some ply and stop it short of the external finish.

 

[John D v2.0]

If you need to extend the fixings out from the uc you can use some ply and stop it short of the external finish.

Thanks Tom, you're a life saver, I can sleep better knowing I have some suggestions for the architect tomorrow! Funny sometimes that someone helping out of the kindness of their heart is more helpful than an architect who's being paid good money.

If you or anyone else think of anything else, I'd be very grateful to hear!

 

[cjard]

You're getting mixed up with aerogel.

AIUI they're quite similar in most regards; lambda, cost, fragility..