How achievable is 3ACH and lower in retrofit

[MikeGrahamT21]

Hi,

 

I'm planning on having an MVHR system at some point in the future, and the bungalow we live in we are renovating room by room. I've seen for MVHR to be really effective anything below 3ACH is required, which seems reasonable, but how achievable is this?

 

Our bungalow has suspended timber floor which I am fully insulating, and then laying an AVCL above the joists, under the floorboards which laps up onto the walls and is getting taped on. The walls are wet plastered without cracks, thickness approx an inch in total. Ceilings are double boarded, both layers plastered. I've sealed up ceiling light wire holes, and intend on doing the same inside the electrical sockets. Paying close attention to the windows and doors in terms of airtightness levels too, getting the best ones i can and the frames are getting taped onto the walls, with foam around the frame as normal.

 

With this approach, what sort of airtightness level would I likely achieve? And if its above 3ACH, what additional measures would I need to take? I appreciate its difficult to guess with all this stuff, and I suppose an air test with smoke pen (or a self air test using a fan in a piece of ply) would be a good way to find anything i've missed.

[Ian]

@MikeGrahamT21

Not sure if this will help but on my (naturally ventilated and min building regs compliance) timber frame new-build bungalow we got a figure of 3.7m3/(m2·h) on the air test without the use of any specific air tightness products - so no special tape or membranes. We had a ground-bearing concrete floor rather than suspended timber. Anything lower than 3.0 and I would have needed MVHR so 3.7 was a result I was happy with.

Edited October 15, 2018 by Ian

[Declan52]

Why not just do all the work you intend and then have the mhrv main use as keeping the air in your house nice and clean. If it recovers some heat then fine. If you have done exceptionally well with all your work and have your house leak free then you will save a bit more.

[AdamSee]

Hi Mike

 

I'm in the same situation as you. Me and my partner are renovating a house and I've gone to quite some lengths to seal off every source of air leakage possible. From a VCL on top of the floor joists downstairs and under the ceiling joists in the bedroom ceiling. Everything has been taped and plastered in to the wall parge coat. We did decided to down the MVHR path, I'm not sure whether at the end of the day we would see the full benefits of the heat recovery, but if you trying to make your house as energy efficient as possible it probably means no trickle vents or random air bricks dotted around, so I assumed that to comply with part F Ventilation we would need something to get in fresh air.

 

After a while you convince yourself that the MVHR makes sense as your going to need the extractor in the bathroom, kitchen and utility, why not just go that one step further? I guess we could have gone down the PIV route, but my wife works from home as a tailor and the heat generated from constantly pressing jackets seems too good to waste and the house becomes unbearably stuffy without a good amount of airflow.

 

I guess a blower door test once your finished will give you the answer you need and being a bungalow it shouldn't be to hard to retrofit everything from the loft.

 

Personally im curious to see what ours works at as, as I've dot and dabed walls, hence the parge coat before hand. I just cant get the hang of wet plastering.

[MikeGrahamT21]

20 hours ago, Declan52 said:

Why not just do all the work you intend and then have the mhrv main use as keeping the air in your house nice and clean. If it recovers some heat then fine. If you have done exceptionally well with all your work and have your house leak free then you will save a bit more.

 

Well that is my intention, just dont want to miss any tricks thats all whilst floors are up and work is being done. I would hate to spend thousands on an MVHR system to find its making matters worse.

[Declan52]

Pay attention to where your joists go into the  wall.  You will need some sort of tape to  seal these up. There will be some where you just can't get to and will have to use  expanding foam and fill the gap as best you can. 

[MikeGrahamT21]

19 hours ago, AdamSee said:

Hi Mike

 

I'm in the same situation as you. Me and my partner are renovating a house and I've gone to quite some lengths to seal off every source of air leakage possible. From a VCL on top of the floor joists downstairs and under the ceiling joists in the bedroom ceiling. Everything has been taped and plastered in to the wall parge coat. We did decided to down the MVHR path, I'm not sure whether at the end of the day we would see the full benefits of the heat recovery, but if you trying to make your house as energy efficient as possible it probably means no trickle vents or random air bricks dotted around, so I assumed that to comply with part F Ventilation we would need something to get in fresh air.

 

After a while you convince yourself that the MVHR makes sense as your going to need the extractor in the bathroom, kitchen and utility, why not just go that one step further? I guess we could have gone down the PIV route, but my wife works from home as a tailor and the heat generated from constantly pressing jackets seems too good to waste and the house becomes unbearably stuffy without a good amount of airflow.

 

I guess a blower door test once your finished will give you the answer you need and being a bungalow it shouldn't be to hard to retrofit everything from the loft.

 

Personally im curious to see what ours works at as, as I've dot and dabed walls, hence the parge coat before hand. I just cant get the hang of wet plastering.

Yeah the loft is prime candidate for all of the pipe work and the unit for sure, though we are toying with the idea of a single dormer, so we won't be doing anything like this until we've made a decision on that, but there will still be room either way. All of the windows i'm ordering have no built in ventilation, and I'm trying to get products which have zero or little leakage, using seals like QLon which are far better than their EPDM counter parts. I think I may rig up a blower door once we have as much done as possible, just to catch anything i've overlooked. Our main issue at the moment is the new kitchen which we had built 6 years ago, the plasterer dotted and dabbed, no parge coat and no adhesive round the edges, plus its still not signed off with BC as the electrician did a runner before doing the certs, so I've a feeling i'm going to have to remove everything and start again, and since i'm happy with plastering myself these days, i'll do it the proper way and get bonding coat and a skim on there, which will resolve that.

 

Well as long as i'm on the right tracks, i'm happy with that, just didn't want to do all of this, and then someone say, you should have done x y and z whilst you were at it lol

[MikeGrahamT21]

Just now, Declan52 said:

Pay attention to where your joists go into the  wall.  You will need some sort of tape to  seal these up. There will be some where you just can't get to and will have to use  expanding foam and fill the gap as best you can. 

 

These are all foamed up, but the AVCL sits above this anyway, directly under the floorboards, so shouldn't affect airflow into the room. I was going to go down the route of plastering round them, and then taping, but didn't have the time in the end.

[Declan52]

31 minutes ago, MikeGrahamT21 said:

Yeah the loft is prime candidate for all of the pipe work and the unit for sure, though we are toying with the idea of a single dormer, so we won't be doing anything like this until we've made a decision on that, but there will still be room either way. All of the windows i'm ordering have no built in ventilation, and I'm trying to get products which have zero or little leakage, using seals like QLon which are far better than their EPDM counter parts. I think I may rig up a blower door once we have as much done as possible, just to catch anything i've overlooked. Our main issue at the moment is the new kitchen which we had built 6 years ago, the plasterer dotted and dabbed, no parge coat and no adhesive round the edges, plus its still not signed off with BC as the electrician did a runner before doing the certs, so I've a feeling i'm going to have to remove everything and start again, and since i'm happy with plastering myself these days, i'll do it the proper way and get bonding coat and a skim on there, which will resolve that.

 

Well as long as i'm on the right tracks, i'm happy with that, just didn't want to do all of this, and then someone say, you should have done x y and z whilst you were at it lol

@JSHarris built his own  rig for  doing a blower test from an old car radiator fan.  Not sure he has put the  info on this site but am sure it's in his blog somewhere. 

 

[MikeGrahamT21]

15 minutes ago, Declan52 said:

@JSHarris built his own  rig for  doing a blower test from an old car radiator fan.  Not sure he has put the  info on this site but am sure it's in his blog somewhere. 

 

Yeah I asked him about that a while ago, i've got all the parts on my watch list on ebay ?

[Jeremy Harris]

18 minutes ago, Declan52 said:

@JSHarris built his own  rig for  doing a blower test from an old car radiator fan.  Not sure he has put the  info on this site but am sure it's in his blog somewhere. 

 

 

I think I've already posted the photo's of it here:

 

 

I swapped the original motor in mine for a brushless one, only because the motor fitted to the fan I had was rusted solid.  If you get a fan with a working motor then a cheap speed controller from eBay will do the job just fine.

 

I only used this to look for air leaks in our old house, not to measure the airtightness as such.  It was fine for doing this, as the leaks were pretty easy to find, especially with the fan set to suck air out of the house, so the leaks were all blowing inwards.  Some of them made enough noise to be able to hear them without a problem, others needed tracking down with a combination of smoke (I used some old joss sticks) and a sensitive airflow meter (a Testo, that's now part of the forum loan kit).

 

One near-invisible source of air leaks in our old house were all the wall to ceiling joints.  The plasterboard ceilings were just taped and filled, and there were tiny gaps all long the wall to ceiling joints in every room that had to be sealed.  Another source of leaks were all the switches and socket outlets.  The fact that most were filled with dead woodlice was a good indication as to how big the gaps were around all the cables.  I sealed up most of these up in the loft, where the cable conduit poked up.  I found that easier than trying to seal the cable entries in the back boxes themselves.

[MikeGrahamT21]

13 minutes ago, JSHarris said:

 

I think I've already posted the photo's of it here:

 

 

I swapped the original motor in mine for a brushless one, only because the motor fitted to the fan I had was rusted solid.  If you get a fan with a working motor then a cheap speed controller from eBay will do the job just fine.

 

I only used this to look for air leaks in our old house, not to measure the airtightness as such.  It was fine for doing this, as the leaks were pretty easy to find, especially with the fan set to suck air out of the house, so the leaks were all blowing inwards.  Some of them made enough noise to be able to hear them without a problem, others needed tracking down with a combination of smoke (I used some old joss sticks) and a sensitive airflow meter (a Testo, that's now part of the forum loan kit).

 

One near-invisible source of air leaks in our old house were all the wall to ceiling joints.  The plasterboard ceilings were just taped and filled, and there were tiny gaps all long the wall to ceiling joints in every room that had to be sealed.  Another source of leaks were all the switches and socket outlets.  The fact that most were filled with dead woodlice was a good indication as to how big the gaps were around all the cables.  I sealed up most of these up in the loft, where the cable conduit poked up.  I found that easier than trying to seal the cable entries in the back boxes themselves.

We have a couple of hairline cracks in the living room ceiling plaster, not sure how we will tackle those without some form of messy filler which will then need sanding, I have seen a couple of paint products which claim to fill hairline cracks, maybe they would be better as an undercoat layer. Definitely plan on sealing the switch and socket outlets, i can see those as a major air leak source too, since no rubber seals existed in the 1960s.

[jfb]

It sounds you are doing all the right things and I would not be surprised if you didn't get well below 3 ACH. I did a full renovation on my old stone farmhouse and got a result of 1ach. Like you at the beginning I was not sure whether to go for Mvhr or not but I am glad I did. I had the benefit of doing the whole renovation in one go so easier to deal with tricky ceiling/wall junctions, etc and the more I read up on it the more further lengths I went to. So go for it. Make sure you plan duct runs for the Mvhr as early as possible. I used twinwall flex duct to make it easier.

[lizzie]

I think it was Beattie passive that developed a system to upgrade renovations.  'T cosy' I think they called it, they wrapped the building in insulation and made it airtight. We visited one and it was v good.

[MikeGrahamT21]

Planning on using the 75mm flexible ducting, but trying to find some with a smooth internal bore to reduce noise and any dust collecting. Will plan where the outlets will be, but they are all accessible from the loft space, and will be completed when we decide what we are doing dormer wise, i've a feeling we probably won't do a dormer, in which case everything is getting lifted in the loft, cleaned, re-wired and loft legs putting in to get 300mm insulation in, and the ducting will go in at that point and be buried in the insulation.

[Jeremy Harris]

I think that all the 75mm OD, 63mm ID ducting has a smooth bore.  I used the HB+ stuff and that's got a smooth, white, internal bore, but I'm pretty sure this stuff is all made to the same spec, and just sold with different labels on.

[MikeGrahamT21]

1 minute ago, JSHarris said:

I think that all the 75mm OD, 63mm ID ducting has a smooth bore.  I used the HB+ stuff and that's got a smooth, white, internal bore, but I'm pretty sure this stuff is all made to the same spec, and just sold with different labels on.

 I've found a lot which has the ridging on both the outside and inside, which I'll definitely be staying away from, don't mind paying a little more for a smooth internal bore, and then a couple of manifolds.

[Jeremy Harris]

I'd not go near MVHR ducting with internal ridges; sounds like a nightmare waiting to happen when it ends up trapping dust etc, apart from the reduced performance it would have.  I've never seen 75mm OD air ducting with ridges internally, so it might be useful to name the brands you've seen that I like this.

[AdamSee]

There's a very good chance this is what you may have found: https://hbspecialistsupplies.com/collections/twinwall-drainage

 

(not sure how much this site will appreciate external links, apologies if it dissapears)

 

I found a few sellers who were buying this ducting and selling it as "air duct", you see it all around the motorways for routing cables in so the internal surface is left without a lining and the colours are suppose to reflect what type of cabling is inside. For instances purple and orange is suppose to be data and lighting, but i cant actually remember.

 

Weirdly, this actually says "twinwall" on the website now....I'm sure that wasn't there several months ago, I'm now debating whether my last statement is just a load of bs or can this be used for ducting? It's dam cheap stuff for 50m....

 

Anyone want to set me straight here?

[Cpd]

Just emailed them and they say it’s got a smooth inner bore. 

 

[PeterW]

It’s what I used - downside is that it doesn’t fit any of the standard fittings as is 63/50mm. Detail is here

 

 

[j_s]

As you know Mike I am doing similar. I've gone for blowerproof on all floor to wall joins, wall to ceiling, wall to wall, all blockwork mortar so very little left of the blockwork is visible.

 

All back box interiors are taped, encased in plasterboard adhesive. Plasterboard adhesive on all board perimeters. Upstairs ceilings are all double boarded, first original ceiling is sealed to wall with blowerproof first ,before hand gaps filled with flexible expanding foam and tescon tape above it in the loft.

 

All cable penetrations, foamed if existing and sealed from below if accessible. New cables are put in conduit and using Stoppas to seal them, these are good but don't hold up to well when moving cables for new lights from below and need refitting (get pushed off of the conduit) which is a pain when it comes to the insulation in the loft.

 

It's been going on since April last year and still got 5 rooms to sort and not managed to switch on the mvhr yet as too worried as not all the ducting is covered in insulation (this week hopefully it will be sufficiently covered)

 

Don't forget to make sure insulated cavity closers are used on door and window openings, not just fitted but sealed with no air leaks whatsoever. We fitted or i should say the builder with a bit of my help fitted them using  expanding foam + CT1 or sticks like **** adhesive. Made a difference around our windows that's for sure. Make sure no holes are in the lintels too.

 

For me it's been a massive learning experience and I wish I was less caring and just turn up the heat as the cost has been huge but we like where we live and plan to be here a while.

Edited October 21, 2018 by j_s

[MikeGrahamT21]

15 hours ago, j_s said:

As you know Mike I am doing similar. I've gone for blowerproof on all floor to wall joins, wall to ceiling, wall to wall, all blockwork mortar so very little left of the blockwork is visible.

 

All back box interiors are taped, encased in plasterboard adhesive. Plasterboard adhesive on all board perimeters. Upstairs ceilings are all double boarded, first original ceiling is sealed to wall with blowerproof first ,before hand gaps filled with flexible expanding foam and tescon tape above it in the loft.

 

All cable penetrations, foamed if existing and sealed from below if accessible. New cables are put in conduit and using Stoppas to seal them, these are good but don't hold up to well when moving cables for new lights from below and need refitting (get pushed off of the conduit) which is a pain when it comes to the insulation in the loft.

 

It's been going on since April last year and still got 5 rooms to sort and not managed to switch on the mvhr yet as too worried as not all the ducting is covered in insulation (this week hopefully it will be sufficiently covered)

 

Don't forget to make sure insulated cavity closers are used on door and window openings, not just fitted but sealed with no air leaks whatsoever. We fitted or i should say the builder with a bit of my help fitted them using  expanding foam + CT1 or sticks like **** adhesive. Made a difference around our windows that's for sure. Make sure no holes are in the lintels too.

 

For me it's been a massive learning experience and I wish I was less caring and just turn up the heat as the cost has been huge but we like where we live and plan to be here a while.

 

Yes I spent a lot of time taping the cavity closers to the block work, and also taping all of the holes in the lintels, so that is covered. Also had a lot of fun filling a box lintel with expanding foam.

 

I really think we are going to be many years before we actually get to the MVHR stage, i've 1 newly built room which needs everything taking off and starting again, and another 2 existing rooms, one of which needs taking back to brick, the other which just needs the floor doing (which i'm doing next year). I've placed an order for some Tado radiator thermostats, which individually graph temperature gain and loss per thermostat, i'm hoping to see in plain view, which rooms are done and which aren't.

 

I do sometimes question why i'm going to all this effort when our gas bills are £20 a month, and we are in the house almost constantly. The rooms i have done, do have an unmistakable 'comfortable' feeling about them though, so I still think its worth the effort. I'm really looking forward to MVHR, and i'm certain it will be worth all this effort.