hotnuts21

For the record im now back in the opinion of going for a central main unit, and probably a brink unit, if they ever get back to me! Paul

Thanks both, Lunos does still seem to be around, but im struggling to find many UK sellers, same for all the options really. The BluAir at least has a lot of information available, the Fresh-R website is a bit basic, but all 3 are passivehouse awarded, so should be fairy reliable. @JohnMo how do you find the decentralised system is it worth it? Paul

oh and did you go with them in the end?

I hadnt heard of these, I was going to ask how they compared, but they seem to have a passivehouse award so should be fairly good. Anyone in the UK supply them or is it deal direct?

Hi all, we are still flip flopping between MVHR or not, one of my issues is the recent realisation of how big the units and incoming/outgoing pipes are and where we are realistically put this that isnt the kitchen or office/spare bedroom. But I have recently come across the option of a decentralised MVHR unit which can be used in retrofit projects and fit into the wall, so take up less room. The one we have been looking at is the Blumartin freeair 100 with some cascade fans in some rooms. However there seems to be very little info about this decentralised approach, and two of the freeair units are similar cost to one standard MVHR unit, although there seems to be more monitoring on it. They also only have a 2yr guarantee which always worries me on something you want to last for a long long time. Any thoughts or experiences of this model or decentralised in general? I see there was a post from a few years ago but nothing since.

Thanks, yes thats true, im not sure using the chimney voids is that realistic but I will continue to investigate all options. Thanks 🙂

I'm still tearing my hair out about it! One thing that might be obvious but wasn't to me, is that MVHR essentially just moves air around the house, by extracting it from the kitchens/bathrooms/utilties etc and then using that to warm air being pushed into the bedrooms/lounges. So if the rooms your pulling from are air tight and warm, then pushing warm air into draughtier rooms is less of a problem (than pulling it from the draughty rooms). For some of the rooms im going to seal the chimney up, and then knock through in the attic space to allow for some level of circulation, im also going to vent from my suspended ceilings into the chimneys so air can come in through air bricks and up the chimney, with the chimney and floor being sealed from the rooms so essentially making the room airtight but the voids have a airflow. Also insulating those floors. I haven't settled on a MVHR yet, ive talked to a lot of companies but they seem to gloss over the fact its not airtight, but then quote airtight standards to me, they are also all mega busy, 2-3 months before enquiries are being answered. Essentially though I'm looking at ones which can run at 40% capacity for now, so we can do the back half of the extension house extracting with no problems, and then turn up it up as we add rooms. As it happens, utility, kitchen and 2 of the 3 bathrooms/WC are all in the new build so thats easy enough for us. I'm still totally open to option though 🙂

I think, and I need to research this more, there is some tape that I can put on the bottom of the joists, I can then run the VB up the wall and along the bottom of the joists sticking to this double sided tape, when I install the plasterboard it screws through the tape/vb and self seals the hole, but I need to look into it more, as its only a small area, it means I could also run it up into the skylight well too which is pretty big on a warm roof!

Yep the flat roof has Alutrix600 vapour barrier on the deck, its the bit between the bottom of the joists and the bottom of the deck I was never sure about, whether we cut it round the joists and tape it to the desk of the flat roof. (warm roof buildup on top of the joists). Sounds like I might be onto something

HI AliG, yes that was my worry with the Steel and one of the main reasons I posted on here. I did wonder if just putting insulation on the inside of the timber upto the flat roof would suffice, especially as i have some left over 150mm celotex. I can bring this right down to ceiling and seal all around it with illbruck FM330 air seal foam, I could also run the vapour barrier across the bottom of the joists as well as up the walls. I may well have to loose some space inside the room and insulate on the inside of those beams, we are using sheeps wool elsewhere so might use 50mm thick of that in a plasterboard box along the beam, else i may end up with cold spots on the walls. Its all more work and cost 😞

This may be a silly question but is there a particular expanding foam I should use? One that maybe has better insulation values or expands a lot to ensure I fill the entire length of the beams?

As they say a picture tells a thousand words, so I have attached some photos. I was scrolling through some pics of my warm flat roof build and realised that the end of the building has two uprights timbers which are effectively a cavity now as they are blocked from inside/outside and now the top. Im wondering if I should drill a hole one of these timbers and fill it with expanding foam?? Although they are in line with the roof/floor joist timbers, they will I presume cause a bit of an effect to the heat loss of the building? Also above all the doors and windows the erectors uses square metal box section for the lintels instead of timbers (Prob cheaper at the time) and so therefore again another cause for panic for heat loss and cold bridging. The outside of the TF shell is getting a 60mm thick woodfibre insulation, and I could insulate with PIR the inside of the timber headers (if thats what they are called) but I cant insulate the steel lintels on the inside as thats the plasterboard level. Could I also drill small holes along the steel and fill with expanding foam too? Thoughts?

Dont know if it helps, but we purchased our skylight from Vario by Velux and it came with its own upstand, pre insulated, sized etc. All we need is a hole in the roof and the inside drops down into the hole with a vapour barrier. Paul

Its a good point and one I think I have been wrestling with for a while including some loss of sleep nights. The extension will defo be airtight when its finished, but the rest of the house is a 1908 terrace with 8 fireplaces so it has challenges, however none of the windows have trickle vents. I have plans for most of the chimneys and we are planning to do the house up over the next 4-5 years so by the end of it, it will be pretty much airtight, I think what I have been looking for is a system that I can install now, but 'turn up' in the future as the rest of the house gets added. I could install the ductwork to 95% of the house now without any issues. But as im currently building two warm flat roofs, It makes sense to put the inlet/outlet in now too. I live by the sea so I always wonder how bad the air quality actually is here, but I like the idea of cool air in the summer too. As the extension is a kitchen, bathroom and Utility I am wondering if maybe I just put in a smallish single/two room system and spend the rest of the budget on a decent thermal store hot water tank as we now have solar and battery so switching to electric water might make more sense too. I think I just have more questions haha!!

Hi All, I've had 3 quotes from some well known companies for my MVHR system, but since we started looking at it two years ago one of the quotes has jumped 56% and has taken it beyond our budget. So I can make sure I'm getting a good coverage of quotes (and knowledge/experience), can people recommend any companies they are happy with, this would be for design and supply as I would fit myself, but the design really need thinking about. Not sure if I'm allowed to mention the companies I have spoken too already, so wont. Feel free to PM/Message me if you would like to not post it publicly. One issue I'm having is where the inlet/outlet pipes go and what kind of sizes we are looking at. We live in a Terrace with 80cm thick stone wall so some of the walls are not really an option! Thanks Paul

I think this is a more accurate makup of what we had ended up with.

Yes, as above you need an OSB or similar racking board. In these types of makes up it typically goes on the inside as per mike wye. However it is breathable (although the least breathable of everything in the build up). We decided to add the external wood fibre board as an after thought, so the timber frame was already up and traditional with it on the outside. It is the point of failure/most likely to get damp/moist, but I spoke to Steico technical support and quite a few others all of who said it was fine to do it the way I did the risk was the condensation analysis, but providing we put a good Vapour barrier on the inside of the wall, it will be fine. Which kinda blows my mind because im using OSB for my flat roofs!!

I was considering a SA before reading this thread 🤣 now I'm just confused. Out of interest @Nickfromwales where abouts in Wales are you based?

I have a warm flat roof that abuts up against the second story of our TF extension. I cant seem to find any detailed information on how to attach the epdm to the TF wall at the abutement, and then which laps over what with the EPDM coming up the wall and the breather membrane coming down the wall. thanks Paul

HI Dave, can you point to any info on lapping it down into the walls, im geniunely interested how this works, as its not something ive come across and cant get my head around how you go down below the deck. This video at about 2mins in talks about lapping it up the wall not down, into the roof structure.

Were you able to lap the vapour barriers together, from the bit you insulated inside?

David I think we are both on the same page, maybe just not explaining ourselves clearly ? Your quote above threw me, as the vapour barrier doesnt go inside the existing house, it goes on top of the lower osb under the insulation which is technically outside the house when your building it ? and then up the outside of the wall at the side/back. Ive watched all Steves (london roofer) videos so I hope im on the right track as I plan to install it exactly as he suggests ?

My understanding was that it went under the insulation then up the outside of the wall and upstands to just above insulation/top deck level so it joins up with the epdm essentially encapsulating the insulation (in a warm roof) so no moisture gets in from below or above. But yes I agree I hear its great stuff, once applied to the bottom deck, I think its 5 weeks guaranteed water/weatherproof giving you time to get the insulation and top deck on (essentially a two weekend job).

Cheers @redtop those photos are really handy. To answer your questions @Dave Jones 1,I will be using Alutrix 600 vapour barrier and bring it up above the insulation on the sides to it meets the EPDM where I can. 2,The insulation I am using is celotex xr4150 which according to the celotext tech dept requires 18mm min board above and below the insulation otherwise they wont support/guarantee any issues (not that they do anyway). Plus we want to put sedum/greenroof trays on the roof in the future so it makes sense to have it boarded on top. 3, We also have a rooflight so I was going to use the same 150x40 round the edge of that and bring the VB upto and over the top of that. The velux rooflight has its own upstand which essentially sits on top of the deck, and has its own VB that hangs down, which I can then tape to where it meets the alutrix where its come up and over. The only thing I cant get my head around is if i should put the vertical pir onto the bottom board deck before or after the VB is laid, eg, do I run it up under the celotex and make that part of the flat roof. Im also unsure about the front of the house where the flat roof meets the second story but the wall below continues. Maybe a external corner patch there.

This is great do you have any photos or diagrams of the buildup as you did it by any chance? I only need to overhang one side due to neighbours, but it's perpendicular to the joists which makes the ladder a bit more awkward. Love the idea of using pir below the WF so obvious but didn't think of it, even though I'm using XPS below the DPC floor in the same way