nod Posted November 17, 2018 Share Posted November 17, 2018 I’ve booked the airtightness test for two weeks time We are block and block construction with sash windows While we have sealed evrything off as we have gone along I was wondering what a reasonable test result would be Link to comment Share on other sites More sharing options...
Oz07 Posted November 17, 2018 Share Posted November 17, 2018 Traditional construction with no special attention to detail i.e. Barriers or tape I reckon you will be hitting 3-5. Below 3 you're supposed to have forced ventilation? Keep in mind the passive lot here will have far better scores! Link to comment Share on other sites More sharing options...
Ian Posted November 17, 2018 Share Posted November 17, 2018 @nod Mine was 3.7 without using any special tapes or airtightness membrane however my build was timber frame and timber clad. Did you wet plaster or dry line your inner block wall? Link to comment Share on other sites More sharing options...
Redoctober Posted November 17, 2018 Share Posted November 17, 2018 2 hours ago, nod said: I’ve booked the airtightness test for two weeks time We are block and block construction with sash windows While we have sealed evrything off as we have gone along I was wondering what a reasonable test result would be Spooky, just booked ours for the 27th Nov. Should be interesting. The thing he wanted to know beforehand was our SAP Calculation. Pre-built it was 83 - is that good bad or indifferent I wonder? Link to comment Share on other sites More sharing options...
nod Posted November 17, 2018 Author Share Posted November 17, 2018 2 hours ago, Ian said: @nod Mine was 3.7 without using any special tapes or airtightness membrane however my build was timber frame and timber clad. Did you wet plaster or dry line your inner block wall? No I decided not to wet plaster But dabbed with a continuous band around all sockets and angles I used sixty bags of adhesive and made sure all joints were pointed In my job I use sever thousand bags of Parge each year I’m not sure that there is much bennefit to airtightness As should get behind the board in the first place Link to comment Share on other sites More sharing options...
ProDave Posted November 17, 2018 Share Posted November 17, 2018 The issue with dot and dab, is unless you are vert careful, you can end up making a "plasterboard tent" with the gap between the wall and PB open to cold air e,g in a cold loft space. I encounter this frequently in houses where you remove a socket and a blast of cold icy air comes out of the socket box. Link to comment Share on other sites More sharing options...
j_s Posted November 17, 2018 Share Posted November 17, 2018 Agree with Dave, I found this a major issue with my 10 year old house. But as long as you have made sure your inner block is parged/sealed and sealed all joins above in the loft then dot and dab is fine. 3/4 of my 1st floor rooms are now fixed with 1 bedroom to go. It's crazy how a few small holes affect the house. I don't always find it blowing a gale outside affects the house, the air pressure makes more of a difference in terms of push/pulling the air in and out. The current builder I used got a score of less than 3 on 2 semi detached houses without even trying to seal it all up ( just his normal attention to detail) and it caused issues with building control and forced ventilation, I'm not actually sure how they got round that in the end Link to comment Share on other sites More sharing options...
nod Posted November 17, 2018 Author Share Posted November 17, 2018 2 hours ago, ProDave said: The issue with dot and dab, is unless you are vert careful, you can end up making a "plasterboard tent" with the gap between the wall and PB open to cold air e,g in a cold loft space. I encounter this frequently in houses where you remove a socket and a blast of cold icy air comes out of the socket box. Agreed Dave We do both Many years back when a lot of the builders where moving into DD I didn’t like doing it But if DD is done right it as good as wet plaster We still sand and cement and skim for one small builder But the drying out time is a lot longer Up and till recently we would do school and hospital corridors in hardwall But less and less now with the advent of abito boards and simalar It’s fairly important to run a bead of airtight sealant around where the plasterboard buts against the block prior to dabbing as an exstra measure and dab all the reveals solid also I see what happens on the 30 th Ive never had a problem with the air tests on the commercial stuff Link to comment Share on other sites More sharing options...
Ferdinand Posted November 18, 2018 Share Posted November 18, 2018 May I add a question. Can I say that dot=and-dab was used extensively from say 1975-present? Is there a time period when dot'n'dab started to be used very widely? Is the 'drafts behind plasterboard' thing becoming less of a problem with new build now that air-seal membranes are used more? I ask because for me renovating, it could be one small factor affecting the ease of renovating properties in favour of older, or even solid-walled, ones. There is a similar time-window calculation for eg asbestos. Two that I have done in the last few years have been renovations of 1970-ish properties. One was traditional plaster, and had cavity insulation so I left the walls alone except for a skim. The other was a virtual rebuild. Cheers Ferdinand Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 18, 2018 Share Posted November 18, 2018 It's near-impossible to stop cold air getting behind dot and dab plasterboard without sealing the blockwork, as several tests have shown. The main problem is that blockwork is inherently porous, especially at the corners of mortar joints, so air will flow through and around any slight gap behind the plasterboard, bypassing any insulation that may be in the cavity. Doesn't really matter how you do the dot and dab, this will always be a potential problem, although using continuous beads on all edges and around all openings makes a slight improvement. Parging the blockwork before applying the dot and dab plasterboard is probably the cheapest and quickest fix, as that should seal up any porosity at source. Easy to test to see whether cold air is getting behind the plasterboard, just point a thermal camera at it on a day when there's a cold wind blowing. If it looks like this then you may as well not have bothered putting insulation in the walls: Link to comment Share on other sites More sharing options...
Ed Davies Posted November 18, 2018 Share Posted November 18, 2018 My opinionated opinion: airtightness testing should be done before the insulation, let alone the plasterboard, is installed. 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 18, 2018 Share Posted November 18, 2018 1 minute ago, Ed Davies said: My opinionated opinion: airtightness testing should be done before the insulation, let alone the plasterboard, is installed. The only exception to that might be for a design where the insulation forms an intrinsic part of the airtightness, such as when pressure blown cellulose or a thick layer of a spray foam like Icynene is used. Both these types of insulation are highly resistant to "wind wash", so contribute a fair bit to the airtightness of the structure. 1 Link to comment Share on other sites More sharing options...
Pete Posted November 19, 2018 Share Posted November 19, 2018 On 17/11/2018 at 06:38, nod said: I’ve booked the airtightness test for two weeks time We are block and block construction with sash windows While we have sealed evrything off as we have gone along I was wondering what a reasonable test result would be Who are you using for the air test and roughly what are the costs pls? Link to comment Share on other sites More sharing options...
nod Posted November 19, 2018 Author Share Posted November 19, 2018 I’m using EPS group Nots they all seem to be around £220 Link to comment Share on other sites More sharing options...
scottishjohn Posted November 22, 2018 Share Posted November 22, 2018 when i get to that stage it will be done before all drywalling is fitted --to make it simple to correct any problems if there are any Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 22, 2018 Share Posted November 22, 2018 13 minutes ago, scottishjohn said: when i get to that stage it will be done before all drywalling is fitted --to make it simple to correct any problems if there are any That's normally when it's done, as otherwise it's impossible to fix porosity issues in the structure without ripping the house apart. The exception might be for wet plastered block construction, where the parge and plaster will be very effective at sealing up the natural porosity of the blockwork. Link to comment Share on other sites More sharing options...
scottishjohn Posted November 22, 2018 Share Posted November 22, 2018 1 minute ago, JSHarris said: That's normally when it's done, as otherwise it's impossible to fix porosity issues in the structure without ripping the house apart. you mean its when it should be done --seen a few things on internet where it is done when house is complete ,and masses of sealer stuffed under skirtiing boards etc - which is why I posted Link to comment Share on other sites More sharing options...
Jeremy Harris Posted November 22, 2018 Share Posted November 22, 2018 1 hour ago, scottishjohn said: you mean its when it should be done --seen a few things on internet where it is done when house is complete ,and masses of sealer stuffed under skirtiing boards etc - which is why I posted We went around a few new builds (not self-builds) when we were looking for a builder, and one was in the middle of doing an air test when we arrived (the house failed to meet building regs) and another where the guys were taping up inside in attempt to pass the air test (one of them told me as soon as the boss who was showing us around went off to answer the phone this was their third attempt to pass building regs). Both those were being tested as bare shells, without any lining internally, and before first fix. Link to comment Share on other sites More sharing options...
joe90 Posted November 22, 2018 Share Posted November 22, 2018 Mine will be tested after finishing as the internal airtightness is wet plaster to rendered internal block walls and windows and doors silicone’d to structure. Yet to find out how successful we were ?. Link to comment Share on other sites More sharing options...
Redoctober Posted November 27, 2018 Share Posted November 27, 2018 Update to this thread - we had our Air Test carried out today - 3 days ahead of our moving in date - We achieved a score of 3.9 which we were most impressed with. This figure was a touch "tight" for us as we have no MVHR and do not wish to install one. We needed to get the figure nearer to 5 so the seals around the loft hatch, letter box and flue were "loosened". Final recorded figure came in at 4.9. The test cost us £245 which included his travelling costs from Perth to the Borders. 2 Link to comment Share on other sites More sharing options...
vivienz Posted November 27, 2018 Share Posted November 27, 2018 Good result. There's a lot to be said for a happy medium - our current house feels like a sieve and the new one will suffocate us if we don't get the MVHR going! Link to comment Share on other sites More sharing options...
newhome Posted November 27, 2018 Share Posted November 27, 2018 18 minutes ago, vivienz said: and the new one will suffocate us if we don't get the MVHR going! No pressure on your MVHR installer then ? Link to comment Share on other sites More sharing options...
vivienz Posted November 27, 2018 Share Posted November 27, 2018 1 hour ago, newhome said: No pressure on your MVHR installer then ? Well, he keeps telling me that he's living the dream. Clearly, I'm paying him too much.? 1 Link to comment Share on other sites More sharing options...
PeterW Posted November 27, 2018 Share Posted November 27, 2018 5 minutes ago, vivienz said: Well, he keeps telling me that he's living the dream. Clearly, I'm paying him too much.? He never was very good at sarcasm.... Link to comment Share on other sites More sharing options...
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