Duncan62 Posted April 13 Share Posted April 13 Could you please help me try to find a Thermal Bridge Free (TBF) connection detail? It's for roof rafters as they connect to a lintel above windows in both cases. I want to avoid metal hangers as these are a tremendous Thermal Bridge. I suggested packing out both sides of the I-Beam (red line) with wood and fastening together, then fastening to the lintel (black lines). SE said no. I'm more of a yes man. Link to comment Share on other sites More sharing options...
joe90 Posted April 13 Share Posted April 13 (edited) I am no SE but I cannot see why he said no, seems very practical to me, would be interesting to hear why he said no 🤷♂️. Mind you a thermal bridge only occurs when one side is outside insulation and the other inside!!! Edited April 13 by joe90 Link to comment Share on other sites More sharing options...
Duncan62 Posted April 13 Author Share Posted April 13 1 minute ago, joe90 said: I am no SE but I cannot see why he said no, seems very practical to me, would be interesting to hear why he said no 🤷♂️. QUOTE: "that wouldn't provide a sufficient connection as we'd be relying on nails through a plywood web of the beam and also the fixings would be running parallel to the grain/laminate of the packer which could lead to the packer splitting. The rafter must be vertically supported and laterally restrained to effectively prevent the roof from dropping or spreading." 1 Link to comment Share on other sites More sharing options...
JohnMo Posted April 13 Share Posted April 13 I am confused what thermal bridge you are trying to fix. 52 minutes ago, Duncan62 said: avoid metal hangers as these are a tremendous Thermal Bridge. Are they really? How is your roof insulated? 1 Link to comment Share on other sites More sharing options...
saveasteading Posted April 13 Share Posted April 13 I can't see that your suggestion reduces thermal bridging. It increases the surface area in contact. The SE is right. Some things you should just keep simple and work to standard, proven methods. The web is a weak material with only the role of keeping the flanges apart. It is not to be used for fixing things to. The Original question was about the thermal bridging. Can you explain your concern. Link to comment Share on other sites More sharing options...
Duncan62 Posted April 13 Author Share Posted April 13 1 hour ago, JohnMo said: I am confused what thermal bridge you are trying to fix. Are they really? How is your roof insulated? 32 minutes ago, saveasteading said: The Original question was about the thermal bridging. Can you explain your concern. Insulation: blown cellulose/woodfibre The problem is that the metal hanger will span the I-Beam from inside the thermal envelope towards outside = thermal bridge. (THERM analysis would show as much) Hanger as below but inverted in my case. Also, as we're hanging an I-Beam the hanger would indeed span the whole section, not partially as shown on this solid rafter. Link to comment Share on other sites More sharing options...
Duncan62 Posted April 13 Author Share Posted April 13 38 minutes ago, saveasteading said: I can't see that your suggestion reduces thermal bridging. It increases the surface area in contact. A connection made of wood will form far less of a thermal bridge than a metal one, whatever thickness wood is used. The concern is in the direction: inside the building to the outside of the building. You can hold onto the other end of even a small bit of wood in a fire. You cannot hold onto a small bit of metal in a fire. The heat transfers. Very efficiently. Link to comment Share on other sites More sharing options...
JohnMo Posted April 13 Share Posted April 13 So your insulation is on top of the rafters? That whole area will need to packed with insulation anyway, so still confused where any size of thermal bridge exists. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted April 13 Share Posted April 13 19 minutes ago, Duncan62 said: Hanger as below but inverted in my case. Can you actually get inverted hangers like that? You will need to pack the Web out to the hanger so you can get the full support to the sides of the hanger. Is there any insulation on the outside of the vertical beam the rafter cones down to. If not you could insulated along the outside edge with some pu and get a better overall performance for the overall detail so you don't need to worry about metal hangers. Link to comment Share on other sites More sharing options...
saveasteading Posted April 13 Share Posted April 13 (edited) The amount of heat transfer through the wood then through the metal will be small. If somebody could work out that this might cost £5 per annum in fuel, would you relax about it? Edited April 13 by saveasteading Link to comment Share on other sites More sharing options...
JohnMo Posted April 13 Share Posted April 13 1 minute ago, saveasteading said: cost £5 per annum in fuel I was thinking more like £5 over 10 - 20 years, that whole area needs to be insulated anyway, so no real thermal bridge exists anyway. Link to comment Share on other sites More sharing options...
ADLIan Posted April 13 Share Posted April 13 Can be modelled using 3D thermal modelling (not THERM) but frankly it's such a localised and discrete piece of metal and no doubt will surrounded by insulation it's not worth worrying about. Link to comment Share on other sites More sharing options...
Iceverge Posted April 13 Share Posted April 13 Do you have the original proposed drawings showing the metal hangers? Thermal bridging is really important once you get to high levels of insulation. I would encourage you to download THERM and have a play. It's not too user friendly and won't give you accurate results like @ADLIan says but it does give you a good feel for the situation. I suspect it'll put your mind at ease once you see how little point connections like wall ties matter and how much difference even 25mm of insulation makes to break a thermal bridge Link to comment Share on other sites More sharing options...
ADLIan Posted April 13 Share Posted April 13 Therm won’t do it as it’s a 3D analysis rather than 2D. Link to comment Share on other sites More sharing options...
SteamyTea Posted April 14 Share Posted April 14 19 hours ago, ADLIan said: Can be modelled using 3D thermal modelling LISA will do 3D modelling. And it is free. 1 Link to comment Share on other sites More sharing options...
NailBiter Posted April 14 Share Posted April 14 On 13/04/2024 at 11:11, ADLIan said: using 3D thermal modelling (not THERM) What is the go to software package for doing this? I've been playing with the tools built into ArchiCad trying to learn how they work but it seems that there are a lot of capabilities missing (or I'm not able to find them due to lack of skill / training). 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