MortarThePoint Posted June 27, 2021 Share Posted June 27, 2021 I'm keen to stay on top of the airtightness as I move forward with the 1st fix and beyond. I am new to thinking about most of this for forgive the inexperience. I'm thinking of leakage as being mostly through surfaces and edges/junctions. Surfaces: wet plaster on the blockwork walls (GF and FF) wet plaster on the plasterboard 'walls' and ceilings of the attic liquid screed on GF and FF Windows themselves are constructed with a good L-value and have not trickle vents Edges & Junctions Considering all the junctions between surfaces: Skirting area (GF & FF) - There is a strip of blockwork around the outside of rooms that is below where the plaster will go. This is where the screed expansion strip sticks. I am fitting the expansion strip to the blockwork wall and then taping the membrane that goes under the screed to the skirt of the expansion strip. That leaves a 'gap' between the expansion strip and the blockwork. Narrow but very long. E.g. 10no. 4x4 rooms with a 1/4 mm gap gives an area of 40,000mm2. Has anyone done anything about this? GF ceiling void - I'll use a sealant between the plasterboard and the walls, but that still leaves a 60+ mm high strip of blockwork and the underside of the hollowcore slabs with no airtightness. measures. Window & door frames - I'm considering using a triple action compraband for this, otherwise a membrane with a sticky strip that sticks to the frame and gets plastered over. Below rafters - VCL with taped joints. Ideally run all the way from wall plate to wall plate and taped to the wall plate all round. Tricky as there is a layer of insulation here too (~100mm at attic floor level). Hollowcore - I have attempted to seal the wall cavity ends of the cores of the hollowcore planks. No access realistic now. I'll seal the leaving space ends of the hollowcore where feasible. There are ~10mm dia. drainage holes that pass vertically through the hollowcore. At the top these will be sealed by the screed membrane. At the bottom I'll probably plug then with something porous (e.g. scrunch of mineral wool insulation) Wall plate - covered by plastering of VCL taped to it. Light fittings - If there other junctions listed above are sealed well then these shouldn't matter so much. For down lighters I'll try to use the types of cover that are designed for use with insulation. Sockets - I'd like to seal the cable entries. What have people used for this? I'm not keen on using a mastic type sealant as that would make any future work a nightmare. A sheet material with holes for the wires cut more tightly would be nice. Loft hatches - insulated and sealed loft hatches to be used. Loft hatch frame taped to ceiling VCL before plasterboard being added. Extractor fans/ventilation - Any not constant extractor fans will need to have a spring loaded damper to close them off when not running. Cable and pipe feeds - Spray foam would be the obvious choice. Otherwise mineral wool insulation. Any areas I have forgotten about? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 27, 2021 Share Posted June 27, 2021 Seems to me that some of this is stopping the air that is inside from getting out. What you need to do is stop the air that is outside getting onto the insulation. 55 minutes ago, MortarThePoint said: wet plaster on the blockwork walls (GF and FF) wet plaster on the plasterboard 'walls' and ceilings of the attic 55 minutes ago, MortarThePoint said: Skirting area 56 minutes ago, MortarThePoint said: GF ceiling void 56 minutes ago, MortarThePoint said: Light fittings 56 minutes ago, MortarThePoint said: Sockets 56 minutes ago, MortarThePoint said: Cable and pipe feeds I don't know what method you are constricting with, but assume that the first external layer (be it OSB, Block or Brick) will leak and the windproof wrap is not that good. Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 27, 2021 Author Share Posted June 27, 2021 8 minutes ago, SteamyTea said: Seems to me that some of this is stopping the air that is inside from getting out. A bit confused, isn't that what air tightness is all about, stopping warm air leaving and cold air entering? All the airtightness measures would mean that air is only coming in and out where intended, through the ventilation system. 10 minutes ago, SteamyTea said: What you need to do is stop the air that is outside getting onto the insulation. Taking the rafter insulation as an example, the plan is a ventilated cavity above mineral wool insulation and then a VCL. Air fro outside will get on to the insulation, but hopefully not through or around the insulation to the warm side. 12 minutes ago, SteamyTea said: I don't know what method you are constricting with Brick and block walls. Hopefully that makes airtightness in that area as simple as wet plaster onto the blockwork walls. Link to comment Share on other sites More sharing options...
tonyshouse Posted June 27, 2021 Share Posted June 27, 2021 Under sills and window boards in through, between, over and under floor planks 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 27, 2021 Author Share Posted June 27, 2021 3 minutes ago, tonyshouse said: Under sills and window boards Hopefully resolved by the Compraband, but I expect I may have to use a sticky membrane too. Something like Tescon Profil though difficult to appreciate how much better that is than duct tape. A lot easier to fit with the backing paper. Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 Air tight foam. The proper stuff. Really good. @Russell griffiths can attest to that Link to comment Share on other sites More sharing options...
SteamyTea Posted June 27, 2021 Share Posted June 27, 2021 48 minutes ago, MortarThePoint said: bit confused, isn't that what air tightness is all about, stopping warm air leaving and cold air entering You can make a building airtight with a very well fitted polythene VCL in the inside. But if the external air is allowed to pass through the insulation, your only U-Value is the thickness of the VCL. Why buildings are wrapped in a breathable, but windtight layer on the outside. Then there are all the junctions that are hard to treat, or can easily fail. A squirt of silicone may get you through an airtest, but it is not a long term solution. Brick, block, page coats, render and plastering all fail somewhere, sometime. It is why no one ever retests their houses, ignorance is bliss. I am not having a go at traditional methods, TFs can fail as well, mine had when I moved in. Hard work finding where all the leaks are. Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 27, 2021 Author Share Posted June 27, 2021 (edited) 18 minutes ago, Oz07 said: Air tight foam. The proper stuff. Really good. @Russell griffiths can attest to that A type of spray foam like this? Edited June 27, 2021 by MortarThePoint Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 No I forget the make but it's top notch. Its in the garage I can tell you next time in there. Used it round all Windows underneath window board etc 1 Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 Why are timber frame people never concerned about vermin damage to membrane in walls? I've got membrane above my ceiling and I always think if vermin were to get in there it would be a nightmare. Link to comment Share on other sites More sharing options...
Faz Posted June 27, 2021 Share Posted June 27, 2021 11 minutes ago, MortarThePoint said: A type of spray foam like this? That is what my window installers used (Munster Joinery) - up against the layer of EDPM I installed it should be pretty bombproof - or indeed air proof! Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 Illbruck I think Link to comment Share on other sites More sharing options...
SteamyTea Posted June 27, 2021 Share Posted June 27, 2021 1 hour ago, Oz07 said: Why are timber frame people never concerned about vermin damage to membrane in walls? I've got membrane above my ceiling and I always think if vermin were to get in there it would be a nightmare. Because anti vermin mesh is put into any vents. Called 'best practice design'. Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 I know but if one gets inside through window or open door in summer these are bypassed Link to comment Share on other sites More sharing options...
cwr Posted June 27, 2021 Share Posted June 27, 2021 Illbruck FM330? That's what I used after it being recommend by this forum. 1 Link to comment Share on other sites More sharing options...
Oz07 Posted June 27, 2021 Share Posted June 27, 2021 Yeh great stuff Link to comment Share on other sites More sharing options...
joe90 Posted June 27, 2021 Share Posted June 27, 2021 5 hours ago, Oz07 said: Why are timber frame people never concerned about vermin damage to membrane in walls? another reason I chose brick and block (with bigger cavity). Link to comment Share on other sites More sharing options...
dpmiller Posted June 28, 2021 Share Posted June 28, 2021 11 hours ago, Oz07 said: I know but if one gets inside through window or open door in summer these are bypassed but then they're in the house, not in the frame... Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 28, 2021 Author Share Posted June 28, 2021 At the skirting junction and the ceiling cavity, should I think about some form of sealing paint or put some wet plaster on at an early stage in those areas? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 28, 2021 Share Posted June 28, 2021 What type/s of insulation are you using? Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 28, 2021 Author Share Posted June 28, 2021 50 minutes ago, SteamyTea said: What type/s of insulation are you using? Poly bead (e.g. Ecobead) cavity wall insulation with Cavalok cavity closers. Mineral wool (Knauf) at rafter level. Mineral wool (Knauf) at ceiling level and any flat roof bits. Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 28, 2021 Share Posted June 28, 2021 I went a bit ott with mine but I got a good airtest the other day. Every gap and joint squirted with some form of sealant and then painted over with an airtight paint. 3 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 28, 2021 Author Share Posted June 28, 2021 9 minutes ago, Russell griffiths said: I went a bit ott with mine but I got a good airtest the other day. Every gap and joint squirted with some form of sealant and then painted over with an airtight paint. Looks comprehensive. What was the airtight paint you used? Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 28, 2021 Share Posted June 28, 2021 5 hours ago, MortarThePoint said: Looks comprehensive. What was the airtight paint you used? Various, I had a 25 ltr tin of gas tight paint left over so I used two coats of that, also blower proof paint. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 28, 2021 Share Posted June 28, 2021 5 hours ago, MortarThePoint said: Poly bead (e.g. Ecobead) cavity wall insulation with Cavalok cavity closers. Mineral wool (Knauf) at rafter level. Mineral wool (Knauf) at ceiling level and any flat roof bits. All those allow air to pass through, so making the external walls of the building is very important. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now