dry-lining / air tightness, minimal membrane punctures...

timmer3 · 28-04-2009 10:13am #1

[copying this from the DIY forum...]

hi folks. i'm dry-lining a house and take seriously the health concerns of phenolic solutions with the potential to trap moisture in the walls and grow mould etc. so i'm going for breathable and vapour permeable, i.e. a diffusion-open moisture membrane, with an air-tightness membrane also.

i got some great advice from an architect who suggested the following construction:
- air-tight membrane (tyvek) attached to concrete wall
- then fix the joists to the wall
- 100mm rockwool between joists
- vapour membrane (intello plus) on top
- breathable plasterboard (with breathable paint etc)

the logic behind putting the air-tight membrane in the warm side of the insulation is to reduce puncture points caused by the wall joist fixtures. but I’m thinking to myself, it’s going to be riddled with nails from the plasterboard anyway, I know these punctures will be small and the pressure from the board will reduce air-tightness loss... but there’s a risk there anyway to have the air membrane so close to the plaster. I can be very careful when fixing shelves and wardrobes etc but I think it would be easy to lose efficiency over years if someone forgets and pokes a nail in from time to time. Even if I sell the house in 10 years time I’d still like to leave behind a very reliable system.

could anyone comment on moving both membranes (not sure if they can be combined into one product) directly on to the concrete wall, and then attach the wall joists directly to the floor and ceiling joists, without any wall fixtures required. Where the membrane wraps into the floor/ceiling it could be taped around the vertical wall joists. this seems a lot safer in terms of the long term risk of puncturing the air membrane. i accept there is a load-bearing issue of resting the weight of the wall on the floor but i can't see it being a massive problem, a few joists and plasterboard.
services and cabling won't cause punctures either way, they will slot in behind the plasterboard regardless.

gsxr1 · 28-04-2009 12:31pm

timmer3 wrote: »

[copying this from the DIY forum...]

hi folks. i'm dry-lining a house and take seriously the health concerns of phenolic solutions with the potential to trap moisture in the walls and grow mould etc. so i'm going for breathable and vapour permeable, i.e. a diffusion-open moisture membrane, with an air-tightness membrane also.

i got some great advice from an architect who suggested the following construction:
- vapour membrane (intello plus) attached to concrete wall
- then fix the joists to the wall
- 100mm rockwool between joists
- air-tight membrane (tyvek) on top
- breathable plasterboard (with breathable paint etc)

the logic behind putting the air-tight membrane in the warm side of the insulation is to reduce puncture points caused by the wall joist fixtures. but I’m thinking to myself, it’s going to be riddled with nails from the plasterboard anyway, I know these punctures will be small and the pressure from the board will reduce air-tightness loss... but there’s a risk there anyway to have the air membrane so close to the plaster. I can be very careful when fixing shelves and wardrobes etc but I think it would be easy to lose efficiency over years if someone forgets and pokes a nail in from time to time. Even if I sell the house in 10 years time I’d still like to leave behind a very reliable system.

could anyone comment on moving both membranes (not sure if they can be combined into one product) directly on to the concrete wall, and then attach the wall joists directly to the floor and ceiling joists, without any wall fixtures required. Where the membrane wraps into the floor/ceiling it could be taped around the vertical wall joists. this seems a lot safer in terms of the long term risk of puncturing the air membrane. i accept there is a load-bearing issue of resting the weight of the wall on the floor but i can't see it being a massive problem, a few joists and plasterboard.
services and cabling won't cause punctures either way, they will slot in behind the plasterboard regardless.

why would you use Tyvex as opposed to polythene vapour barrier, behind a slab? If that's what you are suggesting

http://www2.dupont.com/Tyvek_Construction/en_IE/products/dry_lining/index.html

I recently finished A home and used polythene .
What is the advantage to the very expensive Dupont product ?

sydthebeat · 28-04-2009 1:17pm

the air tightness membrane is a nonwoven-fiber structure which resists air infiltration and water intrusion, yet is engineered to readily allow moisture vapor to diffuse through the sheet, helping prevent mold and mildew buildup and wood rot. The fibrous structure is engineered with microscopic pores that readily allow moisture vapor to evaporate but are so small that bulk water and air cannot penetrate.

A vapour barrier is designed not to allow moisture diffusion, so in summer time a process occurs when external temperatures and humidity are higher then internal. This pressure differential forces moisture into a building from the external, and if you have a dry lining system that does not allow this moisture access into the rooms to evaporate off, then it will get trapped at that point in which interstitial condensation will occur... generally this is on the cold face of the insulation, which of course is between timber studs, which will then be caused to rot and mould will begin to form.
The solution to this is to have a vapour control layer, as opposed to a vapour barrier, which has properties which is both diffusion open in summer, and diffusion closed in winter. Calculations needs to be done to show that the dew point occurs within the wall in winter to prevent condensation forming in the insulation. That is why, in my opinion, a denser fiberous material such as rockwool or sheeps wool is more suited to drylining than the poly-products. Because the poly-products have a better thermal conductivity value they pull the dew point a lot closer to the insulation, increaing risk of condensation forming in a non-vented space. Also these petrolchemical products are now beinging to show signs of unsuitability in this and other application. From what ive been told, sei are about to pull support for the use of phenolics in external insulation application because they disintegrate when wet....

Regards having both your air tightness membrane and your vapour control layer in one, i suppose it is possible but it comes down to the location of this membrane, and the risk of puncturing due to construction work.In my opinion, a service cavity can be created betwen the air tightness membrane and the finishing board. The service cavity can allow electricial wirs or rad pipes, if located here. I would also finish the wall using a stronger facing board product such as sasamox or fermacell if planning on hanging rads, or anything heavy (cast iron curtain rails etc). These boards cantake up to 50kg point loads compared to, i think, 20 kg in plasterboard. If loading is not an issue then non-foil backed plasterboard can be used. Do not use foild backed as this is a vapour barrier.

timmer3 · 29-04-2009 12:16am

found a useful diagram on the tyvek web site which has a useful illustration of the solution sydthebeat is talking about (i think). the only difference is that i hadn't planned to have a vented cavity on the cold side of the insulation. given the porous nature of the mass concrete walls in the house i expect (over time) the moisture could travel back out from where it came.

chavis · 05-06-2009 3:17pm

timmer3 wrote: »

[copying this from the DIY forum...]

hi folks. i'm dry-lining a house and take seriously the health concerns of phenolic solutions with the potential to trap moisture in the walls and grow mould etc. so i'm going for breathable and vapour permeable, i.e. a diffusion-open moisture membrane, with an air-tightness membrane also.

i got some great advice from an architect who suggested the following construction:
- air-tight membrane (tyvek) attached to concrete wall
- then fix the joists to the wall
- 100mm rockwool between joists
- vapour membrane (intello plus) on top
- breathable plasterboard (with breathable paint etc)

the logic behind putting the air-tight membrane in the warm side of the insulation is to reduce puncture points caused by the wall joist fixtures. but I’m thinking to myself, it’s going to be riddled with nails from the plasterboard anyway, I know these punctures will be small and the pressure from the board will reduce air-tightness loss... but there’s a risk there anyway to have the air membrane so close to the plaster. I can be very careful when fixing shelves and wardrobes etc but I think it would be easy to lose efficiency over years if someone forgets and pokes a nail in from time to time. Even if I sell the house in 10 years time I’d still like to leave behind a very reliable system.

could anyone comment on moving both membranes (not sure if they can be combined into one product) directly on to the concrete wall, and then attach the wall joists directly to the floor and ceiling joists, without any wall fixtures required. Where the membrane wraps into the floor/ceiling it could be taped around the vertical wall joists. this seems a lot safer in terms of the long term risk of puncturing the air membrane. i accept there is a load-bearing issue of resting the weight of the wall on the floor but i can't see it being a massive problem, a few joists and plasterboard.
services and cabling won't cause punctures either way, they will slot in behind the plasterboard regardless.

Like with all design concepts and materials, dry lining has some limitations too.
These limitations can effectively be counted as disadvantages of the method.
Dry lining is often considered as not equal to brick work. Since brick houses have more substance, dry lining may seem to be less
than good enough to some people who are more traditional.
Additionally, a dry lined structure can’t hold a tall building,
which limits construction to two or three stories.
Plasterboard is not sufficiently impact resistant, and requires a plaster skim to overcome this disadvantage.
Poor sound insulation is another problem with dry lining.
Wet environments will wreck havoc on plasterboard, which limits the capabilities of dry lining to essentially dry environments.

sinnerboy · 05-06-2009 4:35pm

If the concrete wall is essentially dry i.e.
the DPC is in place and effective
the external render coat is free from defects
all rainwater goods are in good condition

Then I don't believe that the tyvek will do anything usefull placed directly onto the blockwork .

Otherwise the spec is fine . If you have the space for it to could do

existing block
100 x 50 studs ( not joists ) with 100 rockwool between
vapour control layer ( as described by Syd )
50 x 50 battens - horizontal with 50 Rockwool bewteen . Locate cables and pipes in the 50 cavity here . Plan your rad brackets , shelves , fitted units , curtains etc to include 18mm plywood locally fixed over reduced batten 32 x 50 .
then NON foil backed plasterboard ( as per Syd's post )

sinnerboy · 06-06-2009 3:10pm

http://constructireland.ie/Articles/Ventilation/How-why-to-achieve-excellence-in-air-tightness.html

ardara1 · 07-06-2009 2:34pm

Timmer - What level of airtightness do you actually want to achieve?

timmer3 · 07-06-2009 3:32pm

hi sinnerboy. thanks for the replies. DPC is fine and the pebbledash render is in good condition. that's a good idea about the plywood to provide structural support, hadn't thought of that.
in terms of what level of air-tightness i'm aiming for, i don't have a target number but i want to make efficient use of the HRV system and save money on heating. i'm not going for passive etc but want to make it a warm house.
i'm currently researching open cell polyurethane foam as a second option. it has one main advantage that is quite compelling, no capacity for puncture and i assume therefore has a longer functional lifespan. if you rely on a membrane, unless you do a proper air-tightness check on your house every few years i expect one has very little way of checking if it is still working properly. perhaps you might notice a higher heating bill but that could be seasonal etc.

sinnerboy · 07-06-2009 7:12pm

timmer3 wrote: »

. in terms of what level of air-tightness i'm aiming for, i don't have a target number .

Target min Q50 5 .

At B Regs min Q50 10 HRV runs at cost neutral . Worse than this - HRV starts to cost because it actually loses heat "through the leaks" .

The more you better Q50 10 - the more energy is saved . Q50 5 is reasonably easy to achieve - thats why I suggest that .

Q 50 3 or better will demand a lot from your specification and site practices .

etcetc · 07-06-2009 11:26pm

sinnerboy wrote: »

If the concrete wall is essentially dry i.e.
the DPC is in place and effective
the external render coat is free from defects
all rainwater goods are in good condition

Then I don't believe that the tyvek will do anything usefull placed directly onto the blockwork .

Otherwise the spec is fine . If you have the space for it to could do

existing block
100 x 50 studs ( not joists ) with 100 rockwool between
vapour control layer ( as described by Syd )
50 x 50 battens - horizontal with 50 Rockwool bewteen . Locate cables and pipes in the 50 cavity here . Plan your rad brackets , shelves , fitted units , curtains etc to include 18mm plywood locally fixed over reduced batten 32 x 50 .
then NON foil backed plasterboard ( as per Syd's post )

Just looking for clarification on the horizontal 50 by 50 batens do you suggest leaving a void i.e no insulation where the pipes/cables are to be located

ardara1 · 07-06-2009 11:31pm

SO many questions on airthightness - but you don't know what target you want to achieve?? -

Scots Building regs don't recommend anything below 7 'till the Holy Grail of 'ZERO CARBON' MUST be achieved. Why? - because once you build the house so tight you have to put a machine into it to keep those living in it healthy - you're not building a house - your building a machine. The machine WILL need maintenance - it will break down - you can't leave the repairs for a month when it happens?

timmer3 · 08-06-2009 12:16am

ardara1 wrote: »

SO many questions on airthightness - but you don't know what target you want to achieve?? -

without trying to be smart, that's why i'm asking for advice. there are plenty of different products out there for air-tightness, and also opposing views on where is best to locate the various vapour/air membranes, not to mention the insulation. i thought it was a fair question! obviously i want to achieve a good 'number' as you put it, 3 or 5 or whatever @ 50 pressure whatevers, but in my own terms that is the same as saying that i want to do a thoroughly good job. i have given a lot of consideration to air-tightness for this renovation and wouldn't like to come across as a simpleton just because i haven't researched the units to measure air-tightness. the fundamentals of the different solutions are what i am currently researching, and there are pros and cons of each. you might say that an intello membrane is kick ass or level 1 or whatever, but if it will inevitably fail and require repair as your post suggests (if i have understood correctly) then i think other solutions deserve a look-in that don't suffer this problem. in my highly inexperienced opinion, it doesn't make sense to install a system that could require removing plasterboard (and hence tiles and shelves, kitchens, bathrooms, not to mention the redecorating) to determine a point of membrane failure. is one expected to gut the house if the membrane fails?
i haven't found much discussion of spray foam solutions in particular (e.g. icynene / sealection) on boards, perhaps they are not highly thought of. the products claim air-tightness, and they are open cell and hence very slightly vapour permeable and hence not conducive to mould growth. and it is an 'all in one' solution. i have yet to find a compelling argument in favour of a membrane/rockwool over spray foam. i've love to hear opinions on this.

timmer3 · 08-06-2009 12:19am

ardara1 wrote: »

once you build the house so tight you have to put a machine into it to keep those living in it healthy - you're not building a house - your building a machine.

i will be putting in HRV if this is what you mean.

sinnerboy · 08-06-2009 10:29am

etcetc wrote: »

Just looking for clarification on the horizontal 50 by 50 batens do you suggest leaving a void i.e no insulation where the pipes/cables are to be located

no - insulate this void too

sinnerboy · 08-06-2009 10:32am

timmer3 wrote: »

i haven't found much discussion of spray foam solutions in particular (e.g. icynene / sealection) on boards, perhaps they are not highly thought of. the products claim air-tightness, and they are open cell and hence very slightly vapour permeable and hence not conducive to mould growth. and it is an 'all in one' solution. i have yet to find a compelling argument in favour of a membrane/rockwool over spray foam. i've love to hear opinions on this.

try this

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=4078&page=1#Item_8

sinnerboy · 08-06-2009 10:40am

timmer3 wrote: »

in my highly inexperienced opinion, it doesn't make sense to install a system that could require removing plasterboard (and hence tiles and shelves, kitchens, bathrooms, not to mention the redecorating) to determine a point of membrane failure. is one expected to gut the house if the membrane fails?

that would be a catastrophic failure of workmanship . pick your guys as carefully as you are proceeding so far .

look to do a pre test - when all plastering is completed - but before decorations and fittings are in place . Ask your air - tester to visit site before plastering to inspect the tape and membranes first . If good care and attention is given on site you may expect to find localized imperfections only . Some minor not extensive re plastering only.

Q50 5 is optimum in my opinion - a good result without over complicating the build .

( In context Passive house would require Q50 - 0.6 ! )

Shorty69664 · 08-06-2009 11:28am

OK, this maybe a stupid question, (as usual) but doesn't most manufacturers of wall insulation boards claim that if the PIR boards are installed correctly, you don't need a vapour control layer.
I hope to be fitting boards myself shortly and the manufacturer says that the facing on the boards "provide a gas and vapour tight barrier, taping and filling the joints on plasterboard finishes in accordance with drylining good practice, will result in a vapour control layer being created".

Going by their claims I wasn't going to fit a Vapour control membrane.

sydthebeat · 08-06-2009 11:46am

Shorty69664 wrote: »

OK, this maybe a stupid question, (as usual) but doesn't most manufacturers of wall insulation boards claim that if the PIR boards are installed correctly, you don't need a vapour control layer.
I hope to be fitting boards myself shortly and the manufacturer says that the facing on the boards "provide a gas and vapour tight barrier, taping and filling the joints on plasterboard finishes in accordance with drylining good practice, will result in a vapour control layer being created".

Going by their claims I wasn't going to fit a Vapour control membrane.

there is a difference between a 'vapour control layer' and a 'vapour barrier'.

a VCL is an intelligent product that can be both vapour open and closed, depending on temp and pressure differentials.
A VB is permanently vapour closed. That is not such a good system to have because in warm summer days (such as last week) when external temps are higher than internal, vapour is pushed into an external wall from teh outside due to higher pressure outside and lower pressure inside. If you have a VB internally, or in a material such as PIR board etc, then this vapour is pushed into the construction as far as this VB, it cannot go any further. it also condenses into moisture in these areas due to both the colder temp in the wall and the build up of moisture laden vapour. This condensation i shappening in a non-vented area and wil eventually lead to mould groth and teh resultant health impact.

a VCL allows the vapour to travel through it to the internal room and be evapourated off because in higher temps it becomes vapour open. In colder temps it acts as a VB....

Foil back insulation boards shouldnt be used in renovation projects if theres a risk of summer interstitial condensation...

MicktheMan · 25-06-2009 2:05am

sinnerboy wrote: »

( In context Passive house would require Q50 - 0.6 ! )

SB,
Not to nitpick but ... the PH value of .6 is in units of ach and not m3/hr/m2.

sydthebeat · 25-06-2009 10:13am

MicktheMan wrote: »

SB,
Not to nitpick but ... the PH value of .6 is in units of ach and not m3/hr/m2.

mick... in my understanding SB is correct...

a q50 figure of 0.6 must be met.. this is in m3/h/m2... (actually in passive house its n50 figure... ever so slightly different to q50)

this then is divided by 20 to give you your air changes per hour.... 0.6/20 = 0.03 ach..... thats passive standard AFAIK (open to correction)

sinnerboy · 25-06-2009 12:46pm

The BRE have determined in the context of domestic houses that Q50/n50 may deemed interchangable .

DEAP tells us to divide Q50 / 20 to get achr

This does not apply in the case of non domestic buildings . NEAP requires n50

To confuse matters - PHPP - requires specifically n50

Q50 - is derived from the surface area (SA ) of the house enclosure . It measure are leakage through that enclosure .
n50 - is derived from the internal volume ( IV ) of the enclosure . It measures the air change rate within the building .

In simple formed 2 storey structure's SA and IV are closely related numerically

If you live in a standard 3-4 bed semi - do the calcs for yourself .

Nit unpicked

.

MicktheMan · 25-06-2009 2:44pm

sydthebeat wrote: »

mick... in my understanding SB is correct...

a q50 figure of 0.6 must be met.. this is in m3/h/m2... (actually in passive house its n50 figure... ever so slightly different to q50)

this then is divided by 20 to give you your air changes per hour.... 0.6/20 = 0.03 ach..... thats passive standard AFAIK (open to correction)

Syd,
the following is how the 2 measurements interact. The Q50 figure (air permeability) is in units of m3/hr/m2, n50 is in air changes per hour (ACH) and both these are derived from the air flow rate measured through the fan at 50 Pa difference between in and outside. The Q50 is the flow divided by the area of the envelope and the n50 is the flow divided by the volume of the building. As you can see, the shape of the building has a bearing on how close these figures are to each other.

Dividing the Q50 figure by 20 is an empiracle formula for converting the permeability at 50 pascals to that at normal differential pressures for input to deap and has nothing to do with the n50 figure for PH certification.

If you are confused by this, you are not alone. I was recently in Germany at the PH institute and this difference in terminology caused a lot of confusion.

etcetc · 18-02-2010 1:19pm

anybody got experience on the super e houses built in wexford recently

if i am correct they put all their efforts for airtightness on the exterior of building and tackle any interior gaps with expanding foam and tapes

http://www.icynene.ie/pdf/Super_E_article.pdf

http://constructireland.ie/articles/0205supere.php

http://www.property.ie/property-for-sale/Super-E-Homes-124-Portside-Rosslare-Harbour-Co-Wexford/450473/

dry-lining / air tightness, minimal membrane punctures...

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