richo106 Posted January 10, 2023 Share Posted January 10, 2023 (edited) 142 Main Street - MVHR.pdfHi All I am at the stage now that I am planning my first fix items, I am DIY'ing my MVHR install but i haven't done one before I have attached my plans for info As you can see the unit will be mounted in the loft and vented out through the roof. I will be planning on having plenty of insulation in the loft I was just after some inspiration of the best way to install/mount the unit in the loft? Would people recommend creating a base to sit the unit on with the manifolds? Would people put noggins between the joists for the ducts to sit on? and guessing all pipes would be below the loft insulation Basically any photos are their MVHR install would be very much appreciated, or point me in the direction of where to find some As always any information/advice greatly appreciated Many Thanks Edited January 10, 2023 by richo106 Link to comment Share on other sites More sharing options...
Iceverge Posted January 10, 2023 Share Posted January 10, 2023 Hi @richo106 A couple of questions. 1. Can't see your attached files I'm afraid . 2. Is it a warm/cold loft? 3. Is it a radial or trunk and branch layout? Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 5 minutes ago, Iceverge said: Hi @richo106 A couple of questions. 1. Can't see your attached files I'm afraid . 2. Is it a warm/cold loft? 3. Is it a radial or trunk and branch layout? 1. I have now attached my layout 2. Planning on having a cold loft 3. Radial Link to comment Share on other sites More sharing options...
Iceverge Posted January 10, 2023 Share Posted January 10, 2023 Sorry more questions. I take it your kit is onsite and ready to go? Is it a trussed or cut roof? What is your airtightness target? Do you have an airtightness detail for the first floor ceiling? You have a couple of issues here, 1. The MVHR unit should be installed inside the thermal envelope. The radial ducting similarly as they will be moving warm air around. Otherwise you will risk condensation and maybe mold in your ducts and unit as well as cold air being blown into the rooms. 2. You have over 20 penetrations through the airtight layer, not impossible to solve but tricky and impossible to get a good result without a solid strategy. 3. The unit needs to be accessible for servicing. 4. The unit is very near to two bedrooms so taking care of noise must be a priority. Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 14 minutes ago, Iceverge said: Sorry more questions. I take it your kit is onsite and ready to go? Is it a trussed or cut roof? What is your airtightness target? Do you have an airtightness detail for the first floor ceiling? You have a couple of issues here, 1. The MVHR unit should be installed inside the thermal envelope. The radial ducting similarly as they will be moving warm air around. Otherwise you will risk condensation and maybe mold in your ducts and unit as well as cold air being blown into the rooms. 2. You have over 20 penetrations through the airtight layer, not impossible to solve but tricky and impossible to get a good result without a solid strategy. 3. The unit needs to be accessible for servicing. 4. The unit is very near to two bedrooms so taking care of noise must be a priority. This is where the answers of a first time house builder/novice comes in: Yes all the kit is on site Not sure on the roof but i will find out My target is 3, it is part renovation/part new build so aiming to get as low as possible Nope, I was just planning on plaster boarding and skimming it (guessing that's not the right answer) Appreciate all the issues raised, you have now got me panicking Have you any suggestions of how to counteract these issues? I can't think of a other suitable location for my unit else where within the property Would creating a warm loft solve this though? I am guessing this would be a lot more costly? Many Thanks Link to comment Share on other sites More sharing options...
Iceverge Posted January 10, 2023 Share Posted January 10, 2023 1 minute ago, richo106 said: My target is 3, it is part renovation/part new build so aiming to get as low as possible Ok, will still need care however. 2 minutes ago, richo106 said: Nope, I was just planning on plaster boarding and skimming it (guessing that's not the right answer) No wrong answers, just a learning process! 3 minutes ago, richo106 said: Appreciate all the issues raised, you have now got me panicking Don't panic! It's only a house after all and most of us are first timers. Just do the best you can. 4 minutes ago, richo106 said: Have you any suggestions of how to counteract these issues? Yup. 4 minutes ago, richo106 said: I can't think of a other suitable location for my unit else where within the property Maybe that cupboard with all the ducting on the first floor. 5 minutes ago, richo106 said: Would creating a warm loft solve this though? I am guessing this would be a lot more costly? Yes, however it may be too late and not worth the hassle. Do you have any pics of the roof as is, including the area to put the unit? Can you include a few of where the internal walls meet the first floor ceiling. What is your central heating system and how do you plan heating your hot water too? At 3 ACH the benefits of MVHR may be marginal and you could save yourself a whole lot of hassle and cash if you were maybe to opt for another ventilation strategy, and your supplier was willing to take the MVHR as a return. Link to comment Share on other sites More sharing options...
Redbeard Posted January 10, 2023 Share Posted January 10, 2023 I think you really, definitely, want an air/vapour-tight layer at FF ceiling level. Detail it with say Intello membrane (See Buildhub Market Place for a cracking bargain!) and air-tightness tape. If you have to have the MVHR unit up there how about 'engineering' an 'MVHR house' ? You decide on the size needed and you stop the insulation for that square/rectangle. Build a stud 'MVHR house' (with a maintenance door) and make it air-tight and well insulated. Don't insulate the bottom (at FF ceil level). It wants to be in the heated envelope. For aesthetic reasons of course you will still have plasterboard across at FF ceil level (golden rule of pragmatic eco-build - the end result must not look stupid!) but there will be no insulation there to impede heat tfr. There will be a good, tight connection between the surrounding loft insul'n and that on the 'walls' and 'roof' of the 'house'. Link to comment Share on other sites More sharing options...
ProDave Posted January 10, 2023 Share Posted January 10, 2023 First thing at this stage is the roof. Think really really hard before the kit goes up, if you can find a way to do the roof as a warm roof. This will make the build far easier, and far better from so many angles, easier to detail air tightness, easier to detail services like MVHR etc as they will all be in a warm space, and not to mention you will have a nice warm loft for storage. To make it a warm roof, once the trusses are up, you insulate above the trusses and then membrane and battens etc. You often insulate between the rafters as well. you will need some proper input from your designer and might need to speak to planning if you are on a tight ridge height limit. Link to comment Share on other sites More sharing options...
MJNewton Posted January 10, 2023 Share Posted January 10, 2023 33 minutes ago, Iceverge said: Don't panic! It's only a house after all and most of us are first timers. Just do the best you can. That should be the BuildHub motto... 1 Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 Please see attached photo of the build that was taking on Sunday, as you can see I am quite away getting a roof on but wanted to be prepared So I feel I am in a good position to make changes to the roof structure as I haven't fully agreed with builder yet, my only concern like everyone at the minute is my ever dwindling budget Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 More than happy to explore the warm roof option as this is the time to do it Without me googling it this morning I didn't know warm/cold roof was such a thing What is a typical make up of a warm roof? Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 (edited) Is the warm part, adding the insulation DIY'able or would this be in the construction of the actually roof? Edited January 10, 2023 by richo106 Link to comment Share on other sites More sharing options...
Redbeard Posted January 10, 2023 Share Posted January 10, 2023 (edited) That's not what I'd call a Warm Roof, whatever the caption says! A 'full' Warm Roof has all the insulation above the rafters. A 'hybrid' WR has some above and some between, but beware of interstitial condensation risk. Edited January 10, 2023 by Redbeard 'insulation' not 'insuation' and 'what I'd call..' Link to comment Share on other sites More sharing options...
ProDave Posted January 10, 2023 Share Posted January 10, 2023 With proper design input you might be able to make it a hybrid roof with not very much insulation above the rafters to minimise height build up. Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 1 minute ago, ProDave said: With proper design input you might be able to make it a hybrid roof with not very much insulation above the rafters to minimise height build up. Where would I get this proper design input? Many Thanks Link to comment Share on other sites More sharing options...
ProDave Posted January 10, 2023 Share Posted January 10, 2023 In my case it was the house designer, an arcitectural technician who specified all the insulation build up and did the intersitial condensation analysis. My original design was for just 25mm wood fibre board over the rafters and 200mm in between them, but I increased that to 100mm over the rafters. Link to comment Share on other sites More sharing options...
Redbeard Posted January 10, 2023 Share Posted January 10, 2023 Agree with @ProDave. You *might* find a manufacturer's tech dept might suggest a lay-up, but I should have thought they would fight shy of 'designing', in terms of the potential liability. Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 Sorry to confirm, but in all your guys opinion would going for a warm roof be the best option? We are planning to have a couple of velux windows (over the bathrooms) and a large sky lantern on the landing flat roof Would this still work with these? Many Thanks Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 2 hours ago, Redbeard said: That's not what I'd call a Warm Roof, whatever the caption says! A 'full' Warm Roof has all the insulation above the rafters. A 'hybrid' WR has some above and some between, but beware of interstitial condensation risk. Could just having insulation between the rafters work? Then an air tight membrane over the top? Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 I have a meeting with the building later in the week, if it is not possible to have a warm roof for any reason. What is my next best option to help solve some of my issues with my MVHR unit being in the loft Many Thanks Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 4 hours ago, Redbeard said: I think you really, definitely, want an air/vapour-tight layer at FF ceiling level. Detail it with say Intello membrane (See Buildhub Market Place for a cracking bargain!) and air-tightness tape. If you have to have the MVHR unit up there how about 'engineering' an 'MVHR house' ? You decide on the size needed and you stop the insulation for that square/rectangle. Build a stud 'MVHR house' (with a maintenance door) and make it air-tight and well insulated. Don't insulate the bottom (at FF ceil level). It wants to be in the heated envelope. For aesthetic reasons of course you will still have plasterboard across at FF ceil level (golden rule of pragmatic eco-build - the end result must not look stupid!) but there will be no insulation there to impede heat tfr. There will be a good, tight connection between the surrounding loft insul'n and that on the 'walls' and 'roof' of the 'house'. You mean something like this for the vapour layer? Obviously some thought would be needed for the MVHR house Link to comment Share on other sites More sharing options...
Mr Punter Posted January 10, 2023 Share Posted January 10, 2023 28 minutes ago, richo106 said: Could just having insulation between the rafters work? Then an air tight membrane over the top? Often I see insulation between rafters plus 50mm rigid insulation under rafters. Link to comment Share on other sites More sharing options...
richo106 Posted January 10, 2023 Author Share Posted January 10, 2023 9 minutes ago, Mr Punter said: Often I see insulation between rafters plus 50mm rigid insulation under rafters. This was my first thought when I thought of warm roof. In my two front bedrooms I am planning on having vaulted ceilings. At the minute my plan for them was: 120mm PIR between the rafters, 50mm PIR over the top taped, vcl membrane and then plasterboarded. I am guessing there is a reason why I can’t do this in my loft space? Or would this be a suitable option? would there be a cheaper alternative to using 120mm PIR between the rafters? I have attached my 1st floor layout, the red area is a flat roof, all the rest is traditional pitched roof Link to comment Share on other sites More sharing options...
Iceverge Posted January 10, 2023 Share Posted January 10, 2023 (edited) It might help if you posted full section drawings of what is proposed so far. It sounds like you may have some insulation on slope as is buy it's unlikely to be a warm roof. You may want to blank out any personal details. Good news is that you're somewhat ahead of the curve here. Budget wise you'd be advised to get a hold of things as soon as possible and start designing out some expense now if you can. Edited January 10, 2023 by Iceverge Link to comment Share on other sites More sharing options...
Mr Punter Posted January 10, 2023 Share Posted January 10, 2023 2 minutes ago, richo106 said: 120mm PIR between the rafters, 50mm PIR over the top taped, vcl membrane and then plasterboarded. You would be better to have the 50mm under the rafters. For the flat section, rigid insulation on the deck, then waterproof membrane. Vent between the tiles and the Tyvek on the pitched section at eaves and dry ridges / hips. No ventilation for flat section as it is a proper warm roof. Link to comment Share on other sites More sharing options...
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