BotusBuild Posted April 2 Share Posted April 2 (edited) TL;DR - Does the aerogel setup in the diagram below make sense? Long version scene setting ramble before you get to the diagram: We have 2 large I-beams each 160mm wide that support one part of the roof. On top of these I-beams is a warm roof setup, on top of which will be a green roof. One is 7100mm long, the other is 6200mm long. The bottom of each I-beam is flush(ish) with the web joists that hang from them. Unfortunately, one end of each beam protudes through the external wall as a 2000mm cantilever support to the roof. This obviously forms two nasty cold bridges which we are doing our best to now mitigate. Between the joists we will be packing with something like mineral wool to stop the heat getting to the joists through that route. Under the I beam, we've decided we will "make a feature" and create a false joist, but we don't want it too deep down from the ceiling. This will also partly assist in breaking up the very large open plan space. So the plan is to put up some aerogel (probably 10mm thick) supported by some PIR, then the plaster board will go round the whole lot. Constructive comments welcome 🙂 Edited April 2 by BotusBuild Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 (edited) PDF of the same diagram Aerogel for roof I-Beam.pdf Edited April 2 by BotusBuild Link to comment Share on other sites More sharing options...
JohnMo Posted April 2 Share Posted April 2 Really would you waste your money on aerogel and the then support it with PIR. The PIR on its own is doing the job. 10mm Aerogel is really adding nothing to reducing the thermal bridge. Just use 60mm PIR or deeper. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted April 2 Share Posted April 2 Or you could put something like EPS on top instead and have a flush ceiling. Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 3 hours ago, JohnMo said: 10mm Aerogel is really adding nothing to reducing the thermal bridge. John, With a larger R-Value surely Aerogel is doing a better job than PIR for the thickness at reducing the effects of the cold bridge. As I said we don't necessarily want to make this false joist too deep a feature. Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 (edited) 2 hours ago, Iceverge said: like EPS on top instead and have a flush ceiling That would mean doing that across the whole ceiling (about 50m2). The rest of the ceiling apart from these two steels is not a cold bridge. Edited April 2 by BotusBuild Link to comment Share on other sites More sharing options...
JohnMo Posted April 2 Share Posted April 2 38 minutes ago, BotusBuild said: John, With a larger R-Value surely Aerogel is doing a better job than PIR for the thickness at reducing the effects of the cold bridge. As I said we don't necessarily want to make this false joist too deep a feature. You have 10mm of aerogel, PIR with the same R value is between 13 and 15mm depending on its spec. And you are adding 40 to 50mm packer, the packer is providing 3x the thermal resistance of the Aerogel - so why bother with the aerogel, just use PIR, it cheaper, easier to work with. 1 Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 I understand. But there is nothing technically wrong with what I have drawn? Link to comment Share on other sites More sharing options...
Temp Posted April 2 Share Posted April 2 10 minutes ago, BotusBuild said: I understand. But there is nothing technically wrong with what I have drawn? Think you might need two layers of plasterboard under the beam to meet fire regs? Otherwise I can't see anything technically wrong. Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 1 minute ago, Temp said: two layers of plasterboard under the beam to meet fire regs Belt and braces I can appreciate - hopefully we'd have escaped the house before those I-beam give up 🙂 Link to comment Share on other sites More sharing options...
kandgmitchell Posted April 2 Share Posted April 2 24 minutes ago, Temp said: Think you might need two layers of plasterboard under the beam to meet fire regs? Otherwise I can't see anything technically wrong. Only if the beam contributed to the overall stability of the building, if it just supports the roof then no fire protection is required. 2 Link to comment Share on other sites More sharing options...
JohnMo Posted April 2 Share Posted April 2 35 minutes ago, BotusBuild said: I understand. But there is nothing technically wrong with what I have drawn? Nothing technical wrong - you gain a max of 5mm compared to PIR, but at the same time state to use a 45 to 50mm packer. Your money, your house, just trying to save you a few hundred pounds, on wasted materials. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted April 2 Share Posted April 2 Rereading this I see you plan on a warm roof over the top of the entire arrangement. I assume you have 150mm+ of insulation up there running over the joists and the. I beam? If that is the case you don't need any insulation at all below the steel. Link to comment Share on other sites More sharing options...
Iceverge Posted April 2 Share Posted April 2 7 hours ago, BotusBuild said: Unfortunately, one end of each beam protudes through the external wall as a 2000mm cantilever support to the roof. This obviously forms two nasty cold bridges which we are doing our best to now mitigate. Between the joists we will be packing with something like mineral wool to stop the heat getting to the joists through that route Sorry rereading it again..... Can you do a sketch? Link to comment Share on other sites More sharing options...
BotusBuild Posted April 2 Author Share Posted April 2 (edited) 49 minutes ago, Iceverge said: Can you do a sketch? of the where the beam extends out beyond the external wall? How about a picture instead? 🙂 The blue circles are where the two I-beams go through the wall. Everything in the direction of the arrow to the right is now warm roof (160mm PIR) - correction, the warm roof is above the I-beam that runs up and down the picture as well and up to those wooden frames on the left. Edited April 2 by BotusBuild Link to comment Share on other sites More sharing options...
JohnMo Posted April 2 Share Posted April 2 That is one overly complex roof. I would be tempted to look at this the other way around. Ignore what's inside the house. So the roof will have insulation above the steel work. Now the only part exposed is that which is overhanging outside. Insulated the overhang steel, much smaller area, you can have a flat ceiling. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now