Judy C Posted October 30, 2019 Share Posted October 30, 2019 Hello Thank you for adding me. I am about to start building a low energy self build in my back garden. I am an architect so have done this for other people but it is much more stressful doing it for yourself. We are using a SIPS frame. I've found some very helpful information on this forum, hopefully I can contribute too. Link to comment Share on other sites More sharing options...
recoveringbuilder Posted October 30, 2019 Share Posted October 30, 2019 Welcome, well you have to get it right don’t you?! Actually not a bad idea for an architect to do their own self build and experience first hand all the trials and tribulations that go along with it, you’ll find this forum a wealth of information and really helpful people who go out of their way to help or even just sympathise with you! Good luck hope it all goes well oh and we like pictures ? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 30, 2019 Share Posted October 30, 2019 24 minutes ago, Judy C said: Hello Thank you for adding me. I am about to start building a low energy self build in my back garden. I am an architect so have done this for other people but it is much more stressful doing it for yourself. We are using a SIPS frame. I've found some very helpful information on this forum, hopefully I can contribute too. Welcome, can you please reply to the PM sent when you joined. Link to comment Share on other sites More sharing options...
ToughButterCup Posted October 30, 2019 Share Posted October 30, 2019 2 hours ago, Judy C said: [...] but it is much more stressful doing it for yourself. [...] Welcome. In relation to stress, some days I quite enjoy it, others , well - it gets me down. But I sure as Hell have learned to stress only about serious stuff. Without BH, I'd have sunk, long ago. It's the sometimes dark humour that helps most. Most of the things I used to stress about are now simple niggles. Like my leaking flat roof Link to comment Share on other sites More sharing options...
SteamyTea Posted October 30, 2019 Share Posted October 30, 2019 Welcome What is your rational for choosing a SIP construction method? Link to comment Share on other sites More sharing options...
Judy C Posted October 30, 2019 Author Share Posted October 30, 2019 We liked the idea of off-site construction (the overall time on site is quite important to us); good levels of airtightness and really good insulation. It also would have been more straightforward had we chosen to project manage ourselves - but in the end we aren't going to do that. Link to comment Share on other sites More sharing options...
SteamyTea Posted October 30, 2019 Share Posted October 30, 2019 4 minutes ago, Judy C said: really good insulation What sort of values are you looking at? Link to comment Share on other sites More sharing options...
Judy C Posted October 31, 2019 Author Share Posted October 31, 2019 0.11 for floor and flat roofs; 0.13 for walls and 0.12 for the roofs. That's with an extra layer of insulation internally. We are aiming for a/c pf around 2... Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 31, 2019 Share Posted October 31, 2019 7 minutes ago, Judy C said: 0.11 for floor and flat roofs; 0.13 for walls and 0.12 for the roofs. That's with an extra layer of insulation internally. We are aiming for a/c pf around 2... When I looked at SIPs, I was concerned that adding internal insulation might create a potential problem with vapour permeability. We had a debate on this, which involved a chap from Kingspan, I think, on this forum's predecessor. The consensus was that a layer of vapour permeable external insulation was a safer option. IIRC, this was the method chosen on a GD show some years ago, where standard SIPs were externally clad with woodfibre bats. Seemed a reasonable option, as it improved the U value a bit, didn't create a potential vapour permeability problem and increased the decrement delay a fair bit. The other issue I looked into at the time was the thermal bridging within SIP roof panels, as at that time, they used internal timber rafters that created a significant thermal bridge between the skins. Link to comment Share on other sites More sharing options...
Judy C Posted November 4, 2019 Author Share Posted November 4, 2019 We are having an internal lining of insulation (having done the all the condensation analysis) which will mitigate almost all the thermal bridging. In our design there are no internal timber rafters - I think these are necessary for longer spans which our's aren't. I think the downside is the lack of thermal mass - we are having a concrete slab above the insulation but that's all. So will be relying on passive measures to cut out high sun and provide effective rapid ventilation in hot weather. Link to comment Share on other sites More sharing options...
Cpd Posted November 4, 2019 Share Posted November 4, 2019 5 minutes ago, Judy C said: I think the downside is the lack of thermal mass ? your very brave to mention those words so soon........ It’s a a bit of a hot subject on this forum but rest assured most of us understand what your talking about! 1 3 Link to comment Share on other sites More sharing options...
Ferdinand Posted November 4, 2019 Share Posted November 4, 2019 Welcome. Every day is a school day here ? . Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 4, 2019 Share Posted November 4, 2019 The relatively low decrement delay from using insulation with a relatively low heat capacity was one thing that made me shift away from SIPs to an alternative closed panel frame system. We ended up with slightly thicker walls, with 300mm of blown cellulose between the skins (400mm in the roof), but the much longer decrement delay has resulted in a house with a thermal time constant that is a fair bit longer than the diurnal period, which keeps the internal temperature nice and stable. We have a concrete slab above 300mm of insulation, but that isn't as big a factor in having a long thermal time constant as the walls and roof, or even the internal plasterboard and plaster. The latter has a surprisingly high heat capacity, higher than that of concrete, so contributes significantly to maintaining an even temperature. Link to comment Share on other sites More sharing options...
redtop Posted November 4, 2019 Share Posted November 4, 2019 On 31/10/2019 at 16:28, Jeremy Harris said: When I looked at SIPs, I was concerned that adding internal insulation might create a potential problem with vapour permeability. We had a debate on this, which involved a chap from Kingspan, I think, on this forum's predecessor. The consensus was that a layer of vapour permeable external insulation was a safer option. IIRC, this was the method chosen on a GD show some years ago, where standard SIPs were externally clad with woodfibre bats. Seemed a reasonable option, as it improved the U value a bit, didn't create a potential vapour permeability problem and increased the decrement delay a fair bit. The other issue I looked into at the time was the thermal bridging within SIP roof panels, as at that time, they used internal timber rafters that created a significant thermal bridge between the skins. don't suppose you have any more information on the GD episode you mentioned so I can track it down? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 4, 2019 Share Posted November 4, 2019 8 minutes ago, redtop said: don't suppose you have any more information on the GD episode you mentioned so I can track it down? It was an odd build, with an oak frame internally (not sure it was even structural) with a SIP structure outside that, with the SIPs clad with wood fibre bats and then lime rendered. The oak frame was superfluous structurally, I think, as IIRC all the structural support was provided by the SIPs around the outside. This presumably allowed the oak to move around, as it will, without causing airtightness problems. I remember it because the finished house didn't look as if it had been built using modern methods of construction, and also because it had a very large brick external chimney (slightly too large for the house, to my eye). I've just been looking around, and I think it may have been series 3, episode 8, "The Traditional Cottage" in Herefordshire. It was a young couple, and IIRC the girls father had an oak frame company. Link to comment Share on other sites More sharing options...
redtop Posted November 4, 2019 Share Posted November 4, 2019 cheers, will watch later Link to comment Share on other sites More sharing options...
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