Green Building Forum - loft steels and thermal bridging?

loft steels and thermal bridging?

number_thirty_three — Mon, 06 Feb 2023 21:50:42 +0000

I'm looking for a bit of guidance on what to do with the steels we've got in our loft space (mid-terrace). We have two steels that span between the party walls. Could anyone guide me on how much of a cold bridge these present, and [assuming they are a cold bridge] whether there are any sensible ways to mitigate its impacts?

A bit more info: On one side, they are adjacent to a converted dormer, so are in effect sat on 'internal' walls. The other side has no dormer and they are therefore sat on a section of that party wall which faces the outside air. We will be (under)hanging the loft floor joists from these two beams.

There is also a steel 'goal post' that is propping up the bricks of the chimney above the roofline. It is an absolutely absurd quantity of steel for the purpose, but it is there - and again there are bricks sat directly onto that goal post. That's against the wall, where I had already determined I would need to insulate a bit - so I expect that will mitigate some (most?) of that cold bridge. But perhaps there's some condensation risk I should consider...

For context: Right back at the start of our retrofit journey, before we moved in, we had the chimneys removed, and our SE suggested we install the steels for the loft conversion given that we had to do steels for the chimney removal anyway. I now understand that we could perhaps have avoided steels completely (I met someone subsequently who has used Glulam) or at least used a thermal break material like foamglas.

Be grateful for any suggestions on this.

Many thanks

loft steels and thermal bridging?

djh — Tue, 07 Feb 2023 12:34:52 +0000

Steels in the roof/loft are fairly unusual I think, so they've probably been added at some point rather than being original. (having now read to the end I see that is the case!) Drawings and/or photographs would help to understand where they are and what they're doing, as well as what might be done thermally.

loft steels and thermal bridging?

tony — Wed, 08 Feb 2023 08:39:32 +0000

If they were mine I would sit them outside the insulation barrier, ie insulate between them and the inside of your home.

loft steels and thermal bridging?

number_thirty_three — Wed, 08 Feb 2023 14:15:18 +0000

Posted By: tonyIf they were mine I would sit them outside the insulation barrier, ie insulate between them and the inside of your home.

The contact points between the steels and the inside of the home will be through timbers in the webbing of the steel, which will then have joists hung between them. The joists will then have a plywood deck laid on them with the finished floor laid on top of that. Where in that set of connections would it be appropriate/feasible to insulate?

I've attached a pic - thanks!

loft steels and thermal bridging?

tony — Wed, 08 Feb 2023 14:45:35 +0000

I would insulate across the ceiling and under the steel beam, insulating between the steel and the ceiling joist with PIR, then up the front of the steel with PIR presuming up to the sloping ceiling then up the slope.

Where the chimney was I would go round them with the same insulation as the wall here will get, in my case using more insulation than specified, wall can be flat or have recessed insulated recesses. Loft storage can be cold and outside the insulation barrier,

Thanks for the pic, I think I would have had the chimney down.

loft steels and thermal bridging?

number_thirty_three — Wed, 08 Feb 2023 16:08:20 +0000

Thanks tony

Posted By: tonyI would insulate across the ceiling and under the steel beam, insulating between the steel and the ceiling joist with PIR, then up the front of the steel with PIR presuming up to the sloping ceiling then up the slope.

Ok I get the idea here, thanks, makes sense. What would you do at the join between the Steel + Masonry (i.e. Steel is sat on padstones within the brick wall) - you've suggested PIR - presume need to leave a ventilated cavity between the end of the PIR + the masonry in that case?

Posted By: tonyThanks for the pic, I think I would have had the chimney down.

Removing the chimney itself wasnt possible - the Council do not permit it as it affects the visuals of the roofline from the street (also, practically speaking, my neighbour still uses his fireplaces, and the other half of the chimney is his!). Hence the requirement for an absurd amount of steel ('gallows brackets' are no longer allowed).

loft steels and thermal bridging?

bhommels — Wed, 08 Feb 2023 19:30:51 +0000

Posted By: number_thirty_three
Posted By: tonyThanks for the pic, I think I would have had the chimney down.

Removing the chimney itself wasnt possible - the Council do not permit it as it affects the visuals of the roofline from the street (also, practically speaking, my neighbour still uses his fireplaces, and the other half of the chimney is his!). Hence the requirement for an absurd amount of steel ('gallows brackets' are no longer allowed).

I'm up against the same thing, with the difference that our neighbour has had the internal bits of the chimney removed. Unfortunately the council gave more weight to their tenant saying the chimney stack should stay than my plea to take the whole thing down. We are going to end up with the situation that both sides will have steels and whatnot to prop up a ton of bricks for decorative purposes. Madness.

I am going to try my hardest to end up with a minimal amount of steel. I'll ask the structural engineer to look into glulam.

loft steels and thermal bridging?

djh — Thu, 09 Feb 2023 18:29:01 +0000

Posted By: bhommelsWe are going to end up with the situation that both sides will have steels and whatnot to prop up a ton of bricks for decorative purposes. Madness.

I am going to try my hardest to end up with a minimal amount of steel. I'll ask the structural engineer to look into glulam.

FWIW, on a building site near us there are three chimney tops lying in the grass, presumably awaiting use in future houses. I expect the chimneys and pots etc are made of fibreglass or something similar and just bolted on to the roof trusses, but I don't know much about how it all works. Maybe replacing your real chimney with a similar fake would be an answer?

loft steels and thermal bridging?

tony — Thu, 09 Feb 2023 22:35:20 +0000

I canâ€™t remember how many chimneys we removed and corbeled back, no RSJ, no gallows bracket no support, often cutting bricks . Then we used to fit gallows brackets which clearly werenâ€™t needed
Now full steel support.

Once I got my engineer to calculate how a cobbled chimney stayed up , building inspector accepted it.

Belt and braces now seems to be the rule. I donâ€™t know of any chimneys that have fallen down but presumably some have?

loft steels and thermal bridging?

bhommels — Thu, 09 Feb 2023 23:23:38 +0000

Posted By: djh I expect the chimneys and pots etc are made of fibreglass or something similar and just bolted on to the roof trusses, but I don't know much about how it all works. Maybe replacing your real chimney with a similar fake would be an answer?

Thanks, I looked at that but removing one side of a mirrored chimney stack on a party wall was advised against even by the structural engineer on my payroll. There is perhaps a chance of discussing with BR folks to see what we can do with fibreglass and matching brick slips. I'm not holding my breath though.

loft steels and thermal bridging?

djh — Sat, 11 Feb 2023 16:35:07 +0000

Posted By: bhommels
Posted By: djhI expect the chimneys and pots etc are made of fibreglass or something similar and just bolted on to the roof trusses, but I don't know much about how it all works. Maybe replacing your real chimney with a similar fake would be an answer?

Thanks, I looked at that but removing one side of a mirrored chimney stack on a party wall was advised against even by the structural engineer on my payroll. There is perhaps a chance of discussing with BR folks to see what we can do with fibreglass and matching brick slips. I'm not holding my breath though.

I wasn't thinking about just one side. I would talk to your neighbour and replace the whole lot. They could then remove their steels as well.

loft steels and thermal bridging?

bhommels — Sat, 11 Feb 2023 20:15:54 +0000

Posted By: djhI wasn't thinking about just one side. I would talk to your neighbour and replace the whole lot. They could then remove their steels as well.

Sorry, I wasn't very clear. That was my first point of call but neighbour did not want to go with that (not sure why). I then started to explore options of getting as much of my part of the chimney removed as possible, which turns out to be not as much as I'd like.

loft steels and thermal bridging?

lineweight — Fri, 31 Mar 2023 11:54:49 +0100

I'm currently looking at some steel-propped chimneys. This inevitably creates cold bridges, unless you can arrange things such that your steel structure is outside the insulation envelope, which is not an option here.

I'm wondering whether to suggest a course of foamglass or similar between the steel and the retained chimney brickwork. Has anyone seen this done successfully? Does it make things significantly harder to build? I am imagining the chimney is simply propped a course or two higher than would normally be the case, and the gap between steel and propped brickwork filled in with foamglass blocks.

loft steels and thermal bridging?

lineweight — Fri, 31 Mar 2023 12:01:00 +0100

Posted By: number_thirty_threeI'm looking for a bit of guidance on what to do with the steels we've got in our loft space (mid-terrace). We have two steels that span between the party walls. Could anyone guide me on how much of a cold bridge these present, and [assuming they are a cold bridge] whether there are any sensible ways to mitigate its impacts?

A bit more info: On one side, they are adjacent to a converted dormer, so are in effect sat on 'internal' walls. The other side has no dormer and they are therefore sat on a section of that party wall which faces the outside air. We will be (under)hanging the loft floor joists from these two beams.

There is also a steel 'goal post' that is propping up the bricks of the chimney above the roofline. It is an absolutely absurd quantity of steel for the purpose, but it is there - and again there are bricks sat directly onto that goal post. That's against the wall, where I had already determined I would need to insulate a bit - so I expect that will mitigate some (most?) of that cold bridge. But perhaps there's some condensation risk I should consider...

For context: Right back at the start of our retrofit journey, before we moved in, we had the chimneys removed, and our SE suggested we install the steels for the loft conversion given that we had to do steels for the chimney removal anyway. I now understand that we could perhaps have avoided steels completely (I met someone subsequently who has used Glulam) or at least used a thermal break material like foamglas.

Be grateful for any suggestions on this.

Many thanks

What you're describing is a common dilemma in loft conversions. The way I see it you are always faced with the question of whether your general strategy is to insulate outside of the steel structure, or inside of it. Usually, either option creates some cold bridge situations that are difficult to resolve, and it's a matter of deciding per project which is going to create the fewest problems.

I tried to instigate a thread on this general issue here:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16793&page=1