Hi

We have a lot on a small island in coastal BC where we are planning an off grid 4 season vacation cabin (1300 sq feet).   Most of the time the cabin will be unheated and it is a windy wet place in the winter.   Although I want to build with SIPs for high insulation value, the use of OSB worries me as there will be wind driven water.   No one around the Vancouver area seems to make plywood SIPs which would seem more appropriate. 

The other problem with SIPS is that we can't bring a crane in to install large panels.    I'm leaning towards a staggered stud wall instead, with rain screen (drainage plane) plywood sheathing, spray foam on the inside of the sheathing and cellulose bulk fill.

Any comments on how this sort of wall will work in a damp cool climate?

The other challenge on the site are ants.   They took up residence in my neighbours styrofoam insulation and chewed it to bits.   I won't go on about the otters, one winter they moved into the fiberglas batting tacked under the floor up on posts, the smell (think rotten herring!) and the shredded insulation everywhere.

Cheers, Graham

Graham - Anything left unattended will eventually succumb to nature. Would metal skin SIP's be a better solution for the islands??? Metal SIP's should repel 4 legged critters better than OSB. Termite shields at the sill plate and a barrier of stone/masonry (hard-scape) between the foundation and grass/plants will "help" guard against insects.

What type of foundations are typically installed on the islands? I've been to Salt Spring a few times for vacations. We had such great times that I did not take notice of construction techniques.

John

our supply company is shipping metal SIPs to Trinidad and the Bahamas, will ship soon to Guyana where low cost housing will be left with panels just caulked and used as the finished exterior wall and roof finish.

Foundations usually depend on terrain, slab on grade or masonry/concrete piers

Have you looked into PISF's (Pre Insulated Steel Framing) building systems?  They don't need a crane, go up fast and have very high insulation values.  They do use EPS foam so you would have to pay careful attention to detailing to keep out the ants that you mentioned.

Another building system that might be worth looking at is AAC  (Autoclaved Aerated Concrete).  This system is not allowed for use in construction in California yet due to resistance from established building system suppliers, but I've heard some good things about it such as: light weight, mildew and mold resistant, extremely fire resistant, high insulation value, no off gassing, durable, easy to work with, etc. 

the system we use has performguard treated EPS to repel ants and other critters, also does not need a crane to install

Chris, Rio, John and all. Thanks for all the information

The metal stud EPS modules seems less desirable where salt air and condensation might be issues. Metal wall SIPs may have similar issues but could be appropriate if we used a rain screen and then furring strips to install the intended board and batten cedar siding (our island is a pretty rustic place and wood siding seems to fit best). I wonder though how the furring strips would be attached to the metal without perforating the skin (screws would work, perhaps supplemented with construction adhesive)

The aerated autoclaved concrete (AAC) products look really interesting for a damp, insect favoured site - they make both structural panels (steel reinforced lightweight panels) and insulating panels, but it looks like they have not combined the two yet to make a structural insulating panel to make a complete modular wall product. This website explains thier products.

http://www.mhe-international.com/mhe_por_super_lightweight_autoclaved_aerated_concrete.php

I could see a really nice R20 completely AAC sip modular wall product if they bonded the lower density AAC insulation panels (7lb/cu ft, R20 at 6" with the coated wire mesh reinforced structural panels. You can see the specs for the insulation blocks at:

http://www.mhe-international.com/mhe_por_super_lightweight_autoclaved_aerated_concrete.php

Or maybe we should just standup these AAC insulation blocks on a slab, wrap wire mesh around the structure and spray shotcrete on the exterior to make it a finished wall (we shotcrete everything in the underground mining business ....)

Our site is a bare mossy rock bluff amenable to a slab foundation - most island homes around here are built on small concrete cast piers with 6x6in posts and a wood frame floor.

G.Parkinson;

Having built for years in coastal salt areas, I know from personal experience that the corrosion resistant skins ar a non-issue. It is one of the reasons why we switched to steel some years ago in Florida
A rainscreen is absolutely not necessary as the skin itself is the barrier, there is no way to effectivly attach exterior claddings except to attach with screws.
 
But one does not worry about puncturing the tyvek when attaching siding over conventional wood frame ....which is more suseptable to water intrusion at the puncture, why is that? Every siding or roofing fastener punctures the sheathing , is it somehow better to puncture wood?

AAC panels will work and are lightweight compared to regular concrete but will still need to be crane set.

Chris - Thanks for the vote of confidence in using metal SIP skins in salt air on the coast. I agree that metal roofing seems to work fine, we have a "galv-alum"-painted metal roof on a building near our site that is just fine. I'll look into Metal skin SIPs - never seen any around out here on the "raincoast" (we have had over 25 days of rain this month ...).

What I would like to see is an AAC SIP panel building system that combines something like OSB->PolyUrethane-Reinforced<-AAC.

This would keep the moisture sensitive OSB inside where is appropriate, use the benifits of the high insulating value of foam bonded to the structural outer skin of a reinforced (steel mesh) say 2" or 3" panel of AAC which is not sensitive to moisture like an outer OSB SIP panel wall is.

Graham

Graham.

I live in White Rock and know of the rain you speak.  However, OSB has been a respected building product for years with the vast majority of sheathing or panel installations having no issues.  As with any construction project, proper building science incorporated from the start will eliminate potential long term issues.  Your decision to use a rain screen is a good example of forward thinking and an intregal part of the best method to prevent moisture problems with OSB.  Proper site management will also handle the insect problem whether it be ants or termites.  http://www.agf.gov.bc.ca/cropprot/termite.htm  

Don't let poor installation practices from years past make your SIP skin decision for you.  Go to www.buildingscience.com for more info. 

Regards,
Wayne
Insulspan Delta

Wayne

Our site is much more exposed than a typical suburban lot. A neighbours newly built house was soaked inside over the winter when spray and horizontally driven rain was driven up and under the tiles of an expensive tile roof. Although OSB may work for houses that are always heated, I'm not sure that the intermittent heat in a recreational cabin on our site would ever dry the wall out.

Can Insulspan press exterior grade plywood SIP's now? - I'd be interested in SIPs if you do or if you know who does.

Graham

Graham;

it would make sense to use a SIP that is impervious to water

It's the old Mother nature trade off - a view out of this world but weather to make you pay for it.
It is obvious you are building where every element of your design is critical and interdependent for long term success of the project.
Unfortunately, we do not work with treated plywoods due to the size of our laminating equipment and the limitations posed by the size of treated plywood available.
Graham, give us a call and let's discuss the options.

Wayne
800-726-3510