Can we use foilboard and enviroseal wallwrap together « Alternative Technology Assn Forums

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Can we use foilboard and enviroseal wallwrap together

(14 posts) (6 voices)

Started 5 years ago by kksmith
Latest reply from kksmith

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kksmith
Member

We are exploring options of wall insulation for new build house in Melbourne

Our plan is to use below combination :

Plaster board 13 mm
90 mm timber frame with Bradford hp r2.5 batts
Enviroseal proctor wrap
25mm metal battens
Loxo panels 50 mm thick

Q1) can we beef up insulation by including foilboard or similar product? If yes where should we sandwich it?

Q2) if we replace enviroseal with foilboard, will that cause any condesation?

Q3) people say there should be gap between bulk insulation and sarking paper ? But batts and frames are 90 mm thick so theoretically no gap, I believe that problem is resolved by breathable enviroseal wrap or you still need air gap between enviroseal and batts?

I'll appreciate any help as framework is already finished and only option is to play around with insulation stuff and we don't want to regret later on. Thank you.

Posted Wednesday 26 Apr 2017 @ 1:09:03 pm from IP #
Morbo
Member

Just paint your walls white on the outside, then they are pretty much at ambient temperature. Then some foil somewhere and you are done. This will keep the heat gain from radiation at bay. Heat loss from inside, you have your insulation. Outside the batts maybe the foil, but there is something, if water condenses on the foil, there need to be drainage. There are detaisl on that. I reckon you need to consult someone reg condensation, but a builder will be pretty useless. I am doing this since 125 years (combined experience of his 25 people crew?), and never had any condensation.
You dont have thermal mass though, I guess there will be a slab?

Posted Thursday 27 Apr 2017 @ 12:15:27 am from IP #
kksmith
Member

thanks morbo, yes we have frame on slab.
how about roofing, we have flat roof and using anticon blanket under the metal roof.
do we need sarking paper as well or anticon blanket won't form condensation? atleast that's what bradford rep claims.

Posted Thursday 27 Apr 2017 @ 10:29:36 am from IP #
darrynm
Member

Foilboard is a great product but I think a fair amount of it's r-value comes from the foil part = requires an air gap. Could you use thinner batts to leave ~20mm? Not sure re condensation issues.

Posted Thursday 27 Apr 2017 @ 7:51:35 pm from IP #
Gra
Member

You could "beef up" the insulation by installing foilboard in the following manner:

Plaster board 13 mm
90 mm timber frame with Bradford hp r2.5 batts
Enviroseal proctor wrap
25mm metal battens
Foilboard
25mm battens
Loxo panels 50 mm thick.

If you were to go the above route, get a structural engineer to provide advice on fixings and battens. If you've allowed for the Loxo panels to weightbear on the the slab, space to fit the above in may be an issue. You will also need to address the venting and draining of both cavities as the Foilboard will now become your drainage plane. Also, you'll need to re-assess about how you detail weathertightness around window and door openings with the wider wall. There are alternatives to Foilboard which may save you some space (but my understanding is the two cavities will need to stay, regardless).

I wouldn't direct fix the Foilboard (or similar products) to a timber frame (others may disagree, for sure). Water vapour does need a way out. For the walls, vapour will move through, hit the Foilboard and likely condensate on the inside if it's been cold for a while and the dew point has moved to the inside (generally speaking, insulation only slows the movement of heat / cold). In the past, and even now, condensation has been a hit and miss affair. If the house was 'leaky' to air movement, sometimes vapour/condensation control looked after itself by the (uncontrolled) airflow... and sometimes it didn't. If your plan is to make your house airtight (or the better part of it) then you'll need to deal with water vapour movement. You can also look at options like HRV / ERV / humidity controlled aircon to assist in this. Or open windows (which may defeat what you're trying to achieve).

I think you're correct about the batts; if you're using a breather membrane, having the batts close / touching the membrane is ok.

Posted Friday 28 Apr 2017 @ 1:39:32 am from IP #
Morbo
Member

foilboard only works with the airgaps as specified, so relly the foil and the air gap does the work, not some 10mm of bubble wrap
For the anticon, I have to check now 2 years in if there is moisture. But initially it is pushed down underneath the roof sheet, so air cannot actually get in, no air, no humid air, nocondensation. Last tome I checked, there was no condensation between the metal and the anticon.

Posted Friday 28 Apr 2017 @ 12:46:15 pm from IP #
kksmith
Member

thanks Gra, today i had a chance to view "CSR Building Knowledge Seminar 04 by Jesse Clarke " video link as below
https://youtu.be/A1lvirbKYkE
it's very informative and eye opener for layman like me,

i believe we have to stay away from hard board insulation products unless you batten out twice as you proposed. once you put foilboard or similar you loose the benifit of breathable wraper.

1)another point learnt from that video is, you can use 90 mm thick batts in 90mm frame without worrying about air gap between wrapper and batts. i guess that's the whole idea of breathable wrapper. if you use reflective sarking then you must have gap between batts and sarking paper.

2)my another concern was condensation under the metal roof. we are using anticon blanket under the metal roof, confusion was where the condensation goes? but after watching video i believe we have to add a layer of breathable roof sarking in between anticon blanket and metal roofing. (initially i was thinking to put under the blanket but that's not the case)

pls correct me if i made wrong assumptions about above pointers.

Posted Friday 28 Apr 2017 @ 1:08:59 pm from IP #
Annette
Member

Your first point about the 90mm batts and sarking is incorrect. Nothing to do with breathable vs non breathable sarking. The air gap does matter, it's just annoying to create so most don't bother.

Your comment about roof sarking is incorrect. You don't need another layer on top of the blanket.

Look up the yourhome manual.

Posted Friday 28 Apr 2017 @ 1:21:32 pm from IP #
KayKay
Member

Hi kksmith, I have found this article in the Your Home manual helpful when thinking about insulation, sealing and condensation: http://www.yourhome.gov.au/passive-design/sealing-your-home

It seems to say to me that once you install some kind of rigid insulation in or on your walls (eg foam, or the foilboard), then, if you live in a cold climate, you WILL get condensation forming on the rigid insulation and/ or the studs on the "inside the house" side, and probably remaining there permanently too. To prevent this, you need to put a vapour-proof membrane on the "inside the house" side of the studs just under the plasterboard. You should probably also look at using heat recovery ventilation systems to remove water vapour from inside your house, and painting the plasterboard with a non-breathable paint.

Would appreciate people telling me if I have understood condensation issues correctly or not!

Posted Monday 8 May 2017 @ 2:52:16 am from IP #
kksmith
Member

sorry one more question came into mind:
we have added extra plywood bracing to the outside of framework due to engineering demand.
once we put enviroseal on top of plywood bracing, does it still work as effectively as open framework. this ply bracing is about 4.5mm thick.

Posted Tuesday 30 May 2017 @ 2:10:54 pm from IP #
Gra
Member

Hi kksmith,
It should not be a problem with the ply; from the research I've done, having the (vapour permeable) wrap on the outside of the ply will still get you to where you want to go. I'm in the same situation and will be doing likewise absolutely. Ply is rated as semi-permeable (https://buildingscience.com/documents/information-sheets/info-312-vapor-permeance-some-materials); along with OSB, what you are considering is common in other parts of the world.
Sorry I didn't get back to you on your post 28-April. Been drowning. Funny about that video link; when I first started learning, I saw this one. At the time it was so foreign to me (I was starting at a low knowledge base, for sure) that I set it aside. Seeing it again now gives me some comfort that I'm on the right track for what I wish to achieve with my build.
Your point 1. agree.
Your point 2. I have a buddy laying my (tin) roof. He's a full-time roofer and his plan was for Anticon directly under the roof. I'm now reconsidering this, with the thought that I will add the vapour permeable membrane between the tin and the Anticon. I can't see how it could not be a good thing, so will in all likelihood go with it.

Posted Wednesday 31 May 2017 @ 2:44:47 am from IP #
kksmith
Member

Thanks for clarifying Gra.
Based on Annette respose (28th apr), we changed our mind to not to use sarking / breathable membrane in roof.
but after reading your response, i'm confused again if I. should this membrane in roof or not ?
Hopefully someone in the forum can guide us which option to go with as we'll be putting our roof in a week or so.

Posted Wednesday 31 May 2017 @ 11:15:43 am from IP #
Gra
Member

Hi kksmith
for my situation, I have a 2degree roof pitch and live in an area that's usually windy... and often quite so. The same as I'm applying a waterproof (vapour permeable) membrane behind the rain screen on the walls (vertical timbers on battens to provide a vented / drained / pressure equlaised cavity) I've now decided to apply the membrane behind the roof sheets in the same manner and for the same reasons. To your point, no-one (building designer, thermal assessor, structural engineer, building surveyor) has discussed it, nor specified it, but I feel it's the best way to go. To me it makes sense and fingers-crossed, will let me sleep better on those wet and howling nights. If I were a pro. I'd like to give you formal advice, if for no other reason than I can identify with your position. I have the "luxury" of being an OB, and will only have myself to blame if it all goes sideways. :-/

Posted Friday 2 Jun 2017 @ 8:42:35 am from IP #
kksmith
Member

thanks Gra.
just a quick question did you put permeable membrane as per the video sequence - metal roof --- permeable membrane---- anticon --- batten.
& did you put any thin battens between anticon & membrane.
thanks

Posted Sunday 18 Jun 2017 @ 12:55:45 am from IP #

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