GrumpyBear

Question may seem obvious at first - answer being level with the screed. Ideally I'd like to aim for 50-60mm of screed, and the rest PIR insulation. However he slab is currently anywhere between 160mm and 200mm below FFL at the moment. There are large portions of the slab (total area is 48m2) where I could feasibly get up to 120mm of PIR under the screed. Current plan is to mark out areas that will only accept 100mm, and decide how many extra 20mm and 40mm boards I need to level out the PIR over the entire area so that the UHF and screed is a fairly uniform depth. I can level smaller areas with sand. Any suggestions / comments / reccomendations? Thanks! GB

@Temp My understanding is pretty much the same. This is exactly what I found puzzling. The tapered insulation manufacturer probably has an internal policy to not touch hybrid roofs - so calling it a warm roof allows them to sell me 3k of the stuff! My thinking is that the smart membrane on the internal face will actually protect the panels and structure during the wet trades/screed. I've read time and time again that preventing air leaks into the structure is a much bigger concern than vapour diffusion, so I'm edging towards sealing all the internal panel joints and joist junctions with an airtight liquid membrane (soudatight lq) - then installing a smart membrane on the inside face. Cost wise, the cold roof buildup is similar to the hybrid buildup - only the hybrid gives me 0.08 u value, and tapered internal gutters - whereas the cold roof is a headache detailing wise, and that's where the cost ends up being swallowed.

@Russell griffiths yes, 195mm deep timbers 4 aside, as well as two RSJs perpendicular to each other. Panels sit in-between and are insulated. As for complicated buildup - that was the vented cold roof design by the architect which requires over fascia vents on the internal side of the parapet, along the existing house and even along some sides of the roof lights. Those roofing details strike me as being prone to failure and a potential source of water ingress with driving rain. Not to mention potentially ineffective at venting the roof. SIPs are normally considered a cold roof construction. As far as "needing" the 120mm of PIR - that's what the tapered insulation providers have said is the minimum to avoid interstitial condensation. They are basically shifting the dew point as far away from the SIPs structure as possible.

Hi all, Re-post from the roofing section of the forum. Not had any traction there and hoping I might get some interest here. [Original Post follows] We're currently building a 50m2 rear and side extension using SIPs. The SIPs structure has been completed, and includes a flat roof structure also made with SIPs. To make a long story short, I've been told by various sources that converting the flat roof from a vented cold roof design to a hybrid roof with tapered insulation on top is a feasible, though not officially approved solution. I have had WUFI and DELPHI hygrothermal analyses of the proposed build-up sent to me by smart membrane manufacturers which show that this will work all the way down to 60mm of tapered PIR insulation. The tapered insulation manufacturer has just come back, however, stating that the only AVCL they will permit is above the deck (above the SIPs), that they won't approve the use of their products if another Smart Membrane is used below the panels, and that the minimum thickness should be 120mm of PIR (most of which will end up being between 150mm and 255mm) The problem with this is that the structural panels will be exposed to humidity from below without protection from an AVCL, and will quite likely soak up moisture over time. They are referring to our build-up as warm roof, despite the fact that the panels are insulated and sit between joists. In addition, I'm pretty sure they're using the simpler glaser method dew-point analysis as opposed to the more sophisticated and accurate WUFI analysis. I'm thinking of two options here: 1. Agree to get the tapered insulation with the impermeable membrane above the deck and below the tapered insulation. Seal all panel joins and joists with tape and/or sealant without using a smart membrane on the underside of the panels. 2. As above, but use the smart membrane anyway, as the WUFI (from Partel) and DELPHI (from SIGA) analysis says that it will work. Current build up as proposed is the following: OUTSIDE 1.2mm EPDM tissue backed, PIR tapered insulation (120mm minimum) bituminous vapour check membrane 11mm OSB3 172 grey EPS 11mm OSB3 (optional smart membrane like SIGA Majrex, Intello Plus or Partel Vara Plus) 50mm service void plasterboard INSIDE Happy to attach the analyses if helpful... Many thanks in advance for the input and help. GB

Hi all, We're currently building a 50m2 rear and side extension using SIPs. The SIPs structure has been completed, and includes a flat roof structure also made with SIPs. To make a long story short, I've been told by various sources that converting the flat roof from a vented cold roof design to a hybrid roof with tapered insulation on top is a feasible, though not officially approved solution. I have had WUFI and DELPHI hygrothermal analyses of the proposed build-up sent to me by smart membrane manufacturers which show that this will work all the way down to 60mm of tapered PIR insulation. The tapered insulation manufacturer has just come back, however, stating that the only AVCL they will permit is above the deck (above the SIPs), that they won't approve the use of their products if another Smart Membrane is used below the panels, and that the minimum thickness should be 120mm of PIR (most of which will end up being between 150mm and 255mm) The problem with this is that the structural panels will be exposed to humidity from below without protection from an AVCL, and will quite likely soak up moisture over time. They are referring to our build-up as warm roof, despite the fact that the panels are insulated and sit between joists. In addition, I'm pretty sure they're using the simpler glaser method dew-point analysis as opposed to the more sophisticated and accurate WUFI analysis. I'm thinking of two options here: 1. Agree to get the tapered insulation with the impermeable membrane above the deck and below the tapered insulation. Seal all panel joins and joists with tape and/or sealant without using a smart membrane over the underside of the panels. 2. As above, but use the smart membrane anyway, as the WUFI (from Partel) and DELPHI (from SIGA) analysis says that it will work. Current build up as proposed is the following: OUTSIDE 1.2mm EPDM tissue backed, PIR tapered insulation (120mm minimum) bituminous vapour check membrane 11mm OSB3 172 grey EPS 11mm OSB3 (optional smart membrane like SIGA Majrex, Intello Plus or Partel Vara Plus) 50mm service void plasterboard INSIDE Happy to attach the analyses if helpful... Many thanks in advance for the input and help. GB

Hi all, First-time poster here. Have been looking around at the various (extremely informative) posts on this forum for a little while and thought this would be a good time to start actively posting. We have a single storey kitchen extension project that has been approved by the LA. Our architect has produced building regs level drawings and has been working in close collaboration with a SIPs manufacturer to design an airtight shell. The SIPs design is about to be signed off and scheduled for production. Our foundation engineer has come back with a foundation design and spec and I’m about to get 3-5 quotes for someone to take on the groundworks up to DPC. It might be helpful to attach the architectural plans and foundation designs here? I have a few concerns at this stage which I’ll point out, but I’m sure there will be many more further down road! 1. Is it realistic to seek out a non-vat registered builder to take on the groundworks? Say do the labour as non-vat and purchase the materials myself? My guess is it probably isn’t since I’ve got rather precise specs with little margin for error, particularly on the concrete upstand onto which the panels will sit. 2. When the SIPs panels are due to be delivered, the groundworks need to be finished so that the panels can be installed ASAP. Would a finish date and an LDC clause in the groundworks contract be at all helpful? The LDC would be based on the weekly storage fee the SIPs company charges for changing the delivery date. It’s not a huge amount, but would definitely add up with lengthy delays. 3. What’s the best place to get quotes from? Ratedpeople? Myjobquote? Word of mouth recommendations? A combination of the above? Apart from the obvious (providing plans and specs for the quote, timescales), what information should I be asking for in order to end up with like-for-like quotes? Thanks in advance for the input! GB