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Question from a novice (not sure where to post this). How would you go about blocking up 3 extract fan vents? 2 bathroom extracts (100mm) and 1 kitchen extract (150mm) - I'm having an MVHR system installed next week (retrofit) so I want to remove and block up these 3 vents. (Obviously I'll work on airtightness elsewhere) - Walls are brick and block. - Bungalow so it's all accessible - I'll then have the failed CWI extracted and replaced with EPS beads - overall objective of retrofit is to get rid of condensation and make my home more sustainable (use less energy) Do I need to try and leave a cavity? Would people just use expanding foam? How do I prevent a thermal bridge? Any recommendations of products please? The vents are close to the soffits.

I am in the situation where I am converting a garage with a pitched cold roof above. However I’ve also removed the ‘external’ wall that separated the garage and kitchen. I’m taking the opportunity to improve insulation with IWI in the garage and want to also improve airtightness. I’m happy with the floor-wall, wall-ceiling & wall-window details for VCL/airtightness layer with the garage itself. However I’m not sure what to do when I get to the original house. e.g. Crude line drawn on photo below showing continuous airtightness layer coming up external garage wall on left, under insulation in garage ceiling, under steels (to be insulated). then I arrive at kitchen ceiling with bedroom above. What happens when you have to terminate an airtightness layer in a refurb where not all rooms are being tackled? all I can think to do is apply liquid membrane between joists in GF/FF void to underside of FF chipboard & around joist entries into blockwork. Then tape/seal the membrane from the garage onto the liquid one. My air leakage path becomes up into the bedroom which sounds not great given kitchen has lots of moisture. Or carry the membrane right across kitchen ceiling and terminate midway into the house. Also seems wrong.

Hi all 👋🏼, I wanted to introduce myself and our project as I anticipate I'll be in hot pursuit of the forums thoughts, opinions and experiences in the forthcoming months. We purchased a 3-bedroom 1970's bungalow in August 2022 but had some planing complications due to a parish council policy that attempted to dictate that "a bungalow must stay a bungalow". 15 months later our planning application was finally granted, albeit with some compromises. Here's a few points on what we're attempting... Replace existing roof (& ceilings) entirely, building up the walls ~80cm, adding a new roof with 1.2m increased ridge height and steeper pitch Upstairs will accomodate two bedrooms, bathroom and "breakout area" overlooking hallway void Large single-storey flat roof side and back extension out to locate 65sqm kitchen/diner Complete re-configuration of downstairs layout Complete replacement of heating system (gas will be cut off entirely) New ASHP (current thinking Valliant Arotherm Plus, one-zone, no buffer) UFH all-round on ground floor (retrofit lo-profile UFH on top of the existing slab (Wunda?), insulated/screeded in new extension). Possibly fan convectors in bed-rooms upstairs Complete rewire I would assume MVHR (current thinking is a radial system installed through new posi-joists, manufacturer TBH but will get BCF to design) New solar panels, and battery (current thinking GivEnergy to unlock Octopus Intelligent Flux) New double-glazing all round (Residence R7 probably) also 2.7m high, ~8m wide sliding doors at rear (either Corteso Cor-vision or Minima) The biggest grey-area for us at the moment is how much to focus on/invest in improving the insulation and air-tightness of the existing exterior walls. I'll raise a separate thread for this in due course. Fortunately we were able to leverage a second mortgage and keep our existing home so we don't intend to live in the place whilst the majority of the work is taking place. The properties are only 0.5 mile apart so I am hoping I'll be able to keep a close eye on the build whilst I work from home. We are also intending to do a little of the work our-selves as possible (i.e. fitting MVHR, UFH, painting & decorating, airtightness membrane?, etc). Thanks for having me and in advance for any advice, Ollie Fleet, Hampshire Plans 24 OD - Amendments Combined.pdf Concept Images Existing Images

@ mods not sure if this is the most appropriate section. We don't have a dedicated Airtightness one. Time: 1hr. Cost €60 Materials: 1 X Sheet of OSB or PlY 1 x Used car radiator fan including housing ( I used a lexus IS200) 1 X Roll of Airtightness tape. 1 X length of automotive wire. 2 x Crocodile clips. 2 x wire connectors. Some short wood screws Tools. measuring tape. Jigsaw/circular saw. Pocket Knife. Large 12v powersource. ( I just used my cars battery in situ) Screwdriver Direction. 1. Measure an opening window sash/door of your house. 2. Carefully cut the OSB so that it fits snuggly into the opening and presses evenly against the seals of the window. 3. lay the radiator fan including housing on the sheet of OSB and trace the outline. 4. Carefully cut a hole out of the OSB just slightly smaller than the radiator housing. 5. Screw the housing into the hole such that the edges of the housing are all supported by the OSB. 6. Using Airtight tape seal the edges of the fan. 7. Connect the wires to the crocodile clips leaving enough length to reach your power source. 8. Insert the rig into the window and secure in place. It should fit reasonable snuggly, if it is an outward opening sash the vacuum generated will pull it tight to the seals. Consider using tape or a wedge to hold it in place. DON'T use airtightness tape. It'll stick to the window forever. 9. Connect crocodile clips to the power source. You can simply reverse polarity of the clips to swap between depressurisation and pressurisation. Testing procedure. 1. Close all doors and windows in the house. 2. Temporarily seal up/close all vents. 3. Ensure all combustion appliances are off and isolated such that there is no risk of fumes being drawn into the house. 4. Set the fan to depressurise the house. 5. Methodically go room by room using the back of your hand to detect and seal any leaks. Most are found at junctions between floors, walls and ceilings, sockets, windows and doors and wall chases. 6. Use a lighting candle to visually see any pinhole leaks (the flame will flicker). It's much more successful than smoke. Jamming the candle in a length of rigid electrical saves doing too much climbing and descending of steps. Be careful not to burn the house down!!!!! Outside View Using a candle to check leaks. Official test Final Result

Has anyone managed to find an off the shelf access hatch that can be plastered up to and on top of, that is also of a high standard of airtightness AND has some level of insulation incorporated? I am doing a basement conversion that has service hatches to rest of ground floor underfloor crawl space; house will be fixed up with oodles of insulation and MVHR hence I need something good here. In the absence of finding something off the shelf I will just get a well-gasketed plasterable hatch then inside it fix up a PIR inside a 3x2 carcass that can be screwed or similar to the inner reveal (which will be quite deep). Thanks, Tom

I am pretty confident on what my solution is for my basement problem, but it would be prudent to push it out there for some clarification: Basement roof has been sprayed with Icynene open cell insulation (increased air tightness and likely exaggerated my issue) and since we had the roof and downstairs floorboards exposed, it got obviously wet. Now, the liquid tar which was originally poured in the solum has, in large areas, gone and we have soil exposed, which is damp. My humidity readings are 90+, so reaching saturation levels and we have had severe mould growth (like a white fungicidal alien). I have installed forced ventilation, but, I know that the volume of the basement is way too big to cope for the fans to do anything and mould growth continues in the perfect environment for its growth. To make matters worse, we had a chest freezer in the hall, just beside basement hatch, which was pissing water for heaven knows how long. That water has ran down (always finds a way) and run into the basement and also under my flooring (brand new £55 per m2) which has caused mushrooms to grow in our hallway (cleaned off and pointed my dehumidifier at it). Post basement works, ill lift up the flooring and rectify and moisture that is lying on top of the insulation and vapour barrier that is below the wooden floor (I think the vapour barrier has enabled the freezer water to sit there and struggle to dry out as the engineered wood is sitting on top of it. Below is my plan: 1. Suited and booted with my hepa 3 staged filtered vacuum, I will hoover up all signs of mould and fungus (yes, ill double bag the waste bag of the vacuum, wash down (bleach and appropriate chemicals) vacuum, wash filters etc - I worked in the asbestos removal industry, so well versed on protective measures). 2. The basement floor is immaculately clean, but I'll dust it out again and level of the ground as much as I can in readiness for the pour. 3. I'm gonna install 1000 swg heavy duty polythene on the floor, running it up the dwarf walls and basement columns about 100mm to 150mm, which will act as my vapour barrier. 4. I'm going to then install expanding foam tape around that polythene perimeter prior to concrete pour. 5. I'm going to then pump in concrete and level it all over my basement, ensuring that when it meets with the foundation wall/solum junctions, it touches the expanding foam. 6. Ill leave concrete to set for a few months, then I'll get a dehumidifier down there (every good home should have one) and dry that sucker out to see of my humidity levels have been resolved. 7. Pending humidity levels, I will then staple and tape a vapour barrier over the sprayed icynene filled joists to prevent moisture ingress into the insulation itself. Ill dust walls down, prime and then spray tack and then tescon vana tape vapour barrier to the wall. 8. Ill then look at my ground floor mushroom in the hall issue, by lifting the engineered wood up, do a clean up, dry off, clean down removing any fungal spires with bleach and solution and then dry out with dehumidifier. 9. Cross my fingers.

Hello, I was wondering whether anyone could offer any thoughts or advice about the following threshold detail. I'm actually an architect myself and am working solo, so I don't get the benefit of second opinions. I've always worked on larger schemes at the earlier 'conceptual' stage of projects so my practical knowledge of construction details is a little rusty now. This spring, I'm piloting a digitally-enabled kit-of-parts construction system assembled from cnc-cut plywood or OSB that I've been in the process of developing over the last year. Its just a small garden room, so I'm not too concerned about U-values, but I am trying to achieve airtightness to test out how all the details work before I self build our family home next year. I'll then have it tested to see how airtight it is. So, on to the detail - see image attached. Here's the floor build up from top to bottom: 50mm brick pavers, 10mm mortar bed, 18mm T&G Wisa Ply floated floor, 60mm Rigid insulation, RC slab. I'm thinking I can just secure the concrete threshold piece into a bed of mortar over the floated ply substrate - just like the brick. The DPM coming up the slab edge can fold over and tuck under the threshold piece protecting the exposed edges of ply and insulation. An additional waterproof board will go over the DMP too. The only reason I'm questioning it is because I haven't found many examples of how it is done online and so am relying purely on my knowledge/research and common sense. Anyway, any thoughts greatly appreciated. Thanks

There is another thread like this...butnit deals mainly with a brick and block home. Link here: However I wanted to capture basic logical steps for success and glean some wisdom of things that became hard before I start with the airtightness inside. I'm just finishing up outside of our SIPS house fitting the cladding and plan to move inside to start in around 4 weeks. It's a SIPS kit so naturally less junctions that are difficult to deal E.g where you would have trusses meeting blocks walls etc. I have SIPS panel screwed to sip panel, whilst not airtight hies a long way to close uo gaps. I fitted a tony tray during the kit erection, basic plastic sheet but all I could get on a Sunday but will hopefully simplify that step around joists. I have 900m2 of Intello VCL and 40 rolls of tescon vana on hand but before I start that I was thinking along the steps which seem basic but worth checking. Starting bare house internally OSB: 1) go round and fill all holes (there are some despite it being SIPS) with airtightness foam. 2) fit PIR internally over any ridge beams that are exposed and causing big thermal bridges. 3) Fit extra layer of PIR internally (still debating this) in ceilings 4) Fit VCL. Start from the bottom, staple to wall above laps. Should I tape the top of that layer to wall? Or should I just get the layer above on and then tape the lap? Penetrations - I havent put anything through the walls yet. I really should've done them prior to putting on renderboard and cladding but just hasn't happened. There are some big penetations for MVHR and stove direct air feed and ASHP pipes. The rest are small cables and all drainage goes out through the slab with no roof penetrations. How best to do these? Ideally I'd have done them earlier and I'm aware it'll damage the VCL doing after but I haven't decided absolutely where the final locations are and I dont have the MVHR unit, stove or ASHP yet. I know where they go roughly but would struggle to place these just now. I assume I can just put them through later and then just seal around with airtightness tape easily enough. What other tips and bits and I missing. What can I do before I crack on to ensure success and take the best approach.

Looking for wisdom from this forum on how to maintain an uninterrupted airtight layer between the ground floor and the first floor in our retrofit (solid brick mid terrace). The joists run front to back and on the front we have to do IWI (On the rear we’ll be doing EWI so my assumption is that we have a thermal bridge issue to solve on the front; but the rear won’t be such a challenge). I have seen a few different solutions proposed for this: i) rehang joists on joist hangers ii) create a new wall plate on which to rest the joists iii) support from below, leaving a complete gap between floor and wall iv) employ the “Tony tray” method Options (ii) and (iii) aren’t really suitable for our small footprint, bay window shape and structure. I don’t much fancy option (i) with a brick wall… so am extremely interested in the Tony tray option but haven’t been able to find an example of how to use it in a retrofit… is it possible? Can the airtight (breathable) membrane be wrapped around a joist in situ? And if so how…? Any pointers to diagrams, photos or videos extra appreciated! I can accept maybe not being able to achieve an airtight layer in it’s entirety, but what worries me is leaving the end of the joist getting damp in the brick area, which is beyond the insulation and airtight layer. I plan to use only natural breathable insulation, tho, so maybe my concern is unwarranted? thoughts extremely welcome!

Ok. This is embarrassing but here goes. After some considerable time I finally had an airtightness test done today. I wasn’t expecting a great result because it seemed almost impossible to impress upon the builder and architect what was required and working away during the week I just couldn’t be on site enough to see what was being done. Anyway the guy turned up today and we got a number just below 8. I did notice that we had missed dealing 3 of the MVHR vents so maybe the number would have been 7.5 if that was done. We tried sealing them by sealing the MVHR filters but that didn’t work. I was t expecting 1 as a result but expected a lot better than this. The weird thing is that I have sealed most of the obvious draughts and gone around with an IR camera. I keep a very close eye on our gas consumption. Hot water and the pool use 100kWh a day. When the temperature is around 8-11C outside we use 150kWh for heating and at the recent temps of around 3-4C that goes up to 250kWh. This is giving me gas consumption for heating of around 40,000kWh a year so £900. This is less than my last house which was half the size and 15 years old. So by no means high. So considering the gas consumption and no draught issues maybe I shouldn’t worry but we went around to find the worst draughts. A few things surprised me. The walls with stacks in them got very cold. After he left I check in the loft and the holes in the ceiling were not sealed. They go into a small area of cold loft. The insulation covered them and the loft is not ventilated so I can’t usually feel any air movement up there. But once we depressurised the house air was flowing and getting pulled in around the pipes. I can easily seal this. We also found one gap I had missed sealing in the eaves where there was a gale blowing. The other surprising thing is that we have wooden floors upstairs. When we moved in I checked everywhere for draughts. They were only in a couple of places and I sealed them. But again with the house depressurised it drew cold air through the join in loads of places there has never been an issue. The last big issue I think is two small areas of cold loft off our bedroom. I have been in one of these areas and it is the only place in the house where the top of the cavity is exposed and you can feel wind in the loft. I wonder if air was being drawn through the cavity then into walls and roof spaces connected to these areas. It might have accounted for a massive amount of the rest result. I will speak to the architect on Monday but I suspect that the top of these cavities should be closed irrespective of the impact on the test result. There is also one area where the WC is where I have had the builder take down the ceiling and seal stuff as there very obviously seems to be air getting in behind the walls but I have never beeen able to find the source. This was very obvious when we did the test So I have a poor result but yet heating bills are reasonable and there are no draughts. I will seal the stacks up next week and will have to mastic the skirting to the wooden floors which I had suspected would need done. But I think I need to get those cavities closed, annoyingly there is no access to one of the two areas. Moral of the story is do a test after the shell is built as it is quite difficult to fix now. I suspect I can get down to 4 or 5 but that will be it.

Hi, We have a warm flat roof design. This is causing two issues - Cost and airtightness 1. Cost for the Bauder Thermoplan covering is coming in at just shy of £150/sq metre fitted, based on 145sq metres of roof. Considerably more than I expected. The breakdown is Flat areas £10,000 Perimeters and roof light upstands £6000 Outlets £1000 Drainage channels £4000 A couple of questions spring to mind. Are the numbers quoted online for flat roofs, for totally flat roofs and is it normal to charge for the upstand separately? In fairness the upstand is 3-400mm tall. Are drainage channels actually necessary on top of a fall in the roof? These have been specified by the architect, but I cannot find them in standard details? We have a considerable amount of this type of detail, where the gutter area is priced at over £100 per linear metre by the looks of things. 2. Airtightness. The builder has questioned how we achieve airtightness under the roof as there will be a number of penetrations through the ceiling. Spotlights, cabling and MVHR. He also asked how do we tape the airtightness membrane with nothing above it. My thinking is that either we put airtightness membrane across the joists and then create a service area below so the only penetrations are the MVHR which goes between the joists and could be taped up. The alternative is to use two layers of plasterboard with a service void as it would be easier to seal this for the MVHR penetrations and we would tape the joints and tape the wall membrane to it in the service void. Thoughts? Looks like the airtightness question came up earlier in the year but there were no responses.

I am almost done with filling in all the gaps the builders left before I get my second airtightness test. One job I have been putting off doing, but want to do is the inside of the chimney breast. The idiots put the large coat on the outside of the chimney breast, and did not parge inside it before putting the fire in, despite being asked to a couple of times. It is obviously draughty in there. I cannot figure out exactly where the draught comes from, it might be a number of places. Inspecting it, there is around a 10mm gap at the top under the slab, so that may be allowing air in from the cavity. There are also vertical gaps between the blocks as Porotherm does not have mortar in the vertical joints and various gaps in the corners where it meets the outside wall. There are door frames behind these gaps so they may also be a source of air leakage. I have tried foaming up the largest holes, but having looked at it I cannot foam up all the vertical joints. It is also difficult and messy as I am working through a roughly 400x600 hole at the side and some areas are around 2m away from where I have to work. So I was thinking of using a long brush to try and parge the walls. The area is only around 4-5 square metres so I don't mind about the cost/m of what I use. Just something easy to mix up and that won't drip and run al over the place. It also needs to be able to fill in gaps around 10mm wide. I was thinking of buying this. https://www.amazon.co.uk/Bostik-30812571-Cementone-Render-Repair/dp/B01D8FRGMI/ref=sr_1_1_sspa?keywords=plaster+render&qid=1636887565&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyQko4Q1hRWlU1NFBHJmVuY3J5cHRlZElkPUEwOTQxOTU0WkFYUVJaWFMyUE9IJmVuY3J5cHRlZEFkSWQ9QTA4ODEyNDgzMjFWNEw1U0ZDT1lUJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ== Any thoughts?

I am planning a self-build on a plot that I have approval for a two-storey detached house with basement. The structure is a traditional tiled roof on full fill cavity blockwork walls, rendered on outside and painted, with an external footprint of 7.5 x 9m. Looking at air tightness I can find many guides and products that relate to the sealing the internal structure but I cannot find anything that relates to sealing the externals. My thought is to use the external render to provide the airtight seal, but I cannot find any articles that either promote or dispute this approach. Surely it must be the best solution for as long as the doors/windows and service entries are sealed, whatever happens with electricals/plumbing etc inside is then irrelevant. I would be grateful for any comment or views as to whether this approach will work or not.

We are trying to do our best to create a pretty airtight house.... Our Architect has suggested a joiner made front door. Will this be a huge source of air leakage? We are installing MVHR and ASHP and it will kill performance if the door lets wind through. Our current double glazed french patio doors let a gale blow through on windy days....

Hello, I am going to retrofit MVHR in 1930s semi and this also goes hand in hand with getting new windows. The question is: are windows with airtightness class 3 sufficiently airtight to allow MVHR work efficiently or do I need to get windows class 4? Any experiences?

I had purchased all my tapes from Passive house systems and found them great to deal with. When I realised I had not ordered enough I contacted them to ask if I could purchase one more roll and could they look at the postage as it would make it a very expensive roll! Not only did they apply the discount I had received in the earlier orders they posted it free of charge. ( I have no connection to this company)

If anyone interested I have a 15% off code for airtightness tapes with Passive house systems. The code is 15%aocx, not sure how long this code lasts but I have only just ordered and it worked for me. I have the rep's contact details so if it does not work let me know and I will contact him.

Our window fitters left the site without having fitted the Compriband sealing tape. Today they returned to fettle our door (sticky lock mechanism) and , so I thought, to fit the Compriband. They explained that the Durisol surface was too rough for the Compriband to adhere to - and would therefore not act as an efficient seal; so they hadn't fitted it. The day they were fitted, nobody said anything to me about it. This YT video makes me wonder whether the information I have been given this morning is quite as comprehensive as one should expect. Here's a representative example for how the job has been finished ..... The Durisol is indeed rough. The senior fitter says that we need to make sure that the reveal is a lot smoother before the Compriband will adhere to it. Presumably all I need to do is lay on a smoothe parge coat on the window reveal - or is there another easier quicker way of doing it? Clearly, I need to trim back the expanded foam before I coat the reveal with something. Another instance where simple communication has failed. it would have been easier if they had told me either at the pre-fitting meeting or on the days that the windows were fitted or during the week I have waited for them to return - and I should have asked why the Compriband was not being fitted. That said I'm super-pleased with the windows and doors themselves: Gaulhofer. There's just one niggle. It'll be sooooo easy to lock ourselves out. The doors lock automatically when shut.

I get that masonry wall floor joist hangers are favoured over traditional in-wall fixing of joists in the pursuit of airtight homes but can these hangers cope with 100 years of cyclical loading? Here is my beef. Driving a metal nail into a brittle masonry block to attach a hanger feels like an abuse of such dissimilar materials with long-term failure designed into the fixing. Next add 100 years of 80kg cyclical loading as humans walk around inside the home, stir in some thermal expansion and contraction loads on the hanger attachments and surely after a decade or two the hanger nails will start wobbling in the blocks? Then finally for a laugh apply that process to light thermal blocks. Are my concerns unfounded? The no nonsense commercial builder of a plot nearby has fitted his metal web floor joists direct into the inner blockwork and these blocks are heavy structural blocks I think.

Evening all, Been getting on with some first fit plumbing in the four dormers. This is complicated by the fact that below the floors is outside (well some insulation and then outside) - so pipe work needs to go through the timber frame before going downstairs. See pic. I've got two challenges - soldering whilst not melting anything - including the airtight patch that will go over each pipe. The pipes extend below the floor so its tricky work - I cant just solder and then slide them in. Hope my explanation is ok! My thoughts are: 1. Cut the pipes shorter so I can solder the elbows on away from the frame and then connect the drops. Downside is an extra joint. 2. Use a pushfit elbow - I would need to widen the gap in the timber frame. Not too hard to do but another joint and not too sure on how to seal it. 3. Prob my fav. Cut the hole in the floor boards bigger. Slide pipe away from frame and the airtight patch by say 2", solder, cool down the joint & slide back in. Patch the floor. Does anyone have any other suggestions? Cheers Cc

Dear all, A small number of challenges for a Tuesday evening...... Challenge No 1 Picture 1 The picture below is our fire place The gap between the timber frame and the brick wall is the cavity, so any suggestions how I seal this up so that its (permanently) airtight. Would like to achieve below 2 on the airtight test. I assume some sort of timber bonded in place but I am open to any advice. Challenge number 2 Picture 2 how do I make the chimney 'ceiling' airtight (obviously not the flue) - I know now that I should have poured a slab with the flue set into it rather than use the lintels - hindsight is a great thing, shame you only acquire it after the event :-( Maybe 'plaster' it? Maybe a neat job would be to somehow fill it all in, board & then skim it all? - would look neater. Challenge No 3 Picture 3 On a similar line, the picture below shows a gap that I need to close up. The house has overhangs on both sides - looks nice on plans but they need sealing from the rest of the house since in effect they are external space. I was going to screw some supports either side and then some 1/2" ply to close the gap - would some sealing tape then do the trick with regards to airtightness? Tempted to use some silicone in there as well just for a backup. Challenge No 4 Picture 4 This is the void below our first floor - it needs insulating (otherwise it will be a condensation trap) - but how much? I've got some 140 / 150mm celotex about but its a pain to cut and install & I'd rather send it back for a refund. The other option is to use some 3" celotex (a few sheets kicking about) or since I've got to sound proof it all do I just continue the soundproofing down over the wood? This would be the easiest but I'd rather do the correct thing than something easy! Final challenge! Picture 5 Laid the UFH a week ago - the design required some cutting out - I was going to foam these when I suddenly wondered if it would react with the pipe work (Wunda pipe) - am I being OTT or should I play it safe & put something around them first. I'd prefer that each room screed is separate - hence why I want to fill the cuts up. Cheers for any help / guidance. CC

I'm building a warm roof timber frame house with the airtightness layer at the VCL. In one part of the building the ceiling will be vaulted, and there will be three beams at c.3m above FFL, acting as structural ties between the rafters as well as serving as somewhere to position the lighting. That's six penetrations. In the rest of the house, the ceiling will be normal height so I will need joists to carry it. The easy and obvious way is to fly these across between the rafters at eaves level, adding a fair bit of strength to the building. However that would be an additional 16 penetrations in the airtightness layer, which is more than I would like. Any suggestions for a better way of doing this?