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Posted By: GreenApprenticeHi,I don't think I would compromise the long term plan for the sake of a smaller bill this winter. Either buy some warmer work clothes or turn the heating up. A fan heater in the loft would probably make it comfortable enough to work.
We have bought the DuPont airguard VCL with the plan to put it in the loft on top of the ceiling, over the joists and make fully airtight before adding insulation. Due to the amount and type of work involved in that, it will have to wait until warmer weather. The house is very cold so the thinking is to chuck some insulation up there now which will be quick and will help retain some of our heat. Laying the membrane over that will be simpler than removing this insulation and dipping the membrane between the joists before putting the insulation back.
Thanks.
Posted By: Doubting_ThomasIt's been mentioned on here a few times but I highly recommend this website to test construction build-ups (requires free registration to unlock all the features):https://www.ubakus.de/en/r-value-calculator/" rel="nofollow" >https://www.ubakus.de/en/r-value-calculator/
There's a function that advises on moisture risk. It's the much-criticised Glaser method, so very basic and nowhere near as good as WUFI, but as an initial check for peace of mind it's probably worth your time.
Posted By: Peter_in_Hungary
Is the recycled-plastic insulation loose fill or blanket?
Posted By: GreenApprenticeWe have bought the DuPont airguard VCL with the plan to put it in the loft on top of the ceiling, over the joists and make fully airtight before adding insulation.If you were to use a 'smart' membrane (Pro Clima Intello or similar), rather than the Airguard (which I don't think is), you could probably do this. It's one of the details proposed in a paper from Aarlborg University (but not by Pro Clima, AFAIK) - see p7 of this pdf: https://vbn.aau.dk/files/72606879/Installation_of_vapour_barriers_in_existing_buildings.pdf
Posted By: Mike1You mean fig 10? I've been suggesting that GreenApprentice follows the bottom diagram with regards to the membrane but to continue the insulation over the top of the joists so the membrane is everywhere warm. I'm not sure exactly what his current plan is.Posted By: GreenApprenticeWe have bought the DuPont airguard VCL with the plan to put it in the loft on top of the ceiling, over the joists and make fully airtight before adding insulation.If you were to use a 'smart' membrane (Pro Clima Intello or similar), rather than the Airguard (which I don't think is), you could probably do this. It's one of the details proposed in a paper from Aarlborg University (but not by Pro Clima, AFAIK) - see p7 of this pdf
Posted By: djhYou mean fig 10?Yes, the lower diagram in fig 10. Sounds like we're suggesting the same thing then.
Posted By: Peter_in_Hungary
If you put the air tight membrane over the joists etc. then when the MVHR is put in you will need to properly seal the vents. If the membrane is over the joists it can easily be lifted along with the blanket type insulation, the MVHR easily installed without the need for duct penetrations, then the membrane over the ducts and joists then the insulation over that. i.e. no insulation between the joists and then everything is below the membrane except the insulation which is above.
Just a thought.
Posted By: GreenApprenticethe plan was to do the lower diagram, the difference is that the joists are only 7.5cm deep so there will be a lot of insulation above them. Unfortunately I bought the non-smart version of the airguard membrane, but djh is suggesting that so long as there is insulation above that, which there will be, then it will be okYes, with the insulation it will be fine.
Posted By: GreenApprenticeWe’ll also put a breathable membrane on top of the insulation as suggested by TyvekPresumably then you have a ventilated roof and the aim is to stop wind washing of the insulation. Which sounds fine, if Tyvek claim suitability for that (I've not read their datasheet).
Posted By: GreenApprenticeThoughts on this - if we put something over the joists to support and protect the membrane (like cardboard?) there would be an air gap above the ceiling that the MVHR ducts sit in, with the airtight membrane aboveTwo basic options:
Posted By: Peter_in_Hungary
Will the air tight membrane be sealed at the edges? (of the membrane strips and the edges of the loft) if so how?
Posted By: Peter_in_Hungary
thick(ish) paper will do that without the expense of tyvek
Posted By: djh
I don't know what duct system you're thinking of using, but I can generally recommend semi-rigid, which have a smaller dimension as Mike1 suggests.
Posted By: GreenApprenticePosted By: Peter_in_Hungary
thick(ish) paper will do that without the expense of tyvek
Like lining paper?
Posted By: GreenApprenticeThat’s what we’re going to be using from BPCWhich system? You might want to start another topic to continue this discussion.
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