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leebree
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# Posted: 11 Jun 2013 12:33
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I hope the forum can offer me some advice....
We are about to re-do our wrap-around porch on a lake-front cabin in southern Quebec (Near Namur, QC).
At present the porch is shoddily supported on semi-cantilevered beams that come out of the cottagem and also some makeshift steel posts. But there is sag in the porch decking - and in any case the porch posts and railings are rotting, as well as some of the sub-structure. So it's time for a complete re-do.
We were planning to dig frost-proof footings as you would for a regular deck and build up from there. But the grade at that point is only 2 feet above the water level in the lake (and the lake is only five feet away from the front of the porch!)
There are two issues. Firstly, when we dig down more than two or three feet it's highly likely the holes will flood with water, which poses problems for making regular sonotube-based footings. We will try puming water out before pouring the concrete but there's no guarantee the holes will not collapse.
The second issue is whether these footings would in any case be frost-proof. A local contractor advised us that regular sonotube footings (even with a belled end) would still move with the frost, since the water table is high. He said he would do the following. Dig down as far as possible. Pour a two foot square concrete pad (perhaps 8 or 10 inches thick). Place a treated 6x6 post on top of the cured pad and backfill with dirt. He added that he would bury 2" styrofoam sheets around the post a few inches under grade to reduce the impact of freezing.
Since the porch is covered the area around the posts will not be covered in snow, so the ground will get cold. Normally people dig at least 48" or more to avoid heaving.
I am however a little unwilling to bury 6x6 treated posts, even if they are rated for ground contact (It seems that in Canada we only have two classifications for treatment - above grade and ground contact - we do not have a specific classification for burial).
I would like this to be a solid and long lasting foundation since we'll be putting a lot of work into the decking (which will be cedar BTW) and posts and railings etc.
The dimensions, if relevant, are as follows. The porch is L-Shaped, 54" wide. The long side is 32' and the short side is 17'. I place to create four piers along the long side including the corner, and two more along the short side.
I would be grateful for any advice or thoughts!
thanks in advance....
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leebree
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# Posted: 11 Jun 2013 12:42
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I should add that the cabin, which is 50 years old, is built on a concrete block foundation - but the foundation only goes down three feet or so. (there's a dirt crawl space).
There has been a little movement - a few cracks in the foundation and a slightly sagging central beam - but it's not bad.
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razmichael
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# Posted: 11 Jun 2013 12:55
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No advice to offer on the posts but I will suggest you check (openly or silently) and the regulations building/upgrading so close to the water. The provincial wide rules changed dramatically last year (and have been tougher than some provinces for years). These are the baseline rules - municipalities can make things harder but connect (except by not caring) make them easier. Beside the distance from the water (suspect you are grandfathered in) no pressure treated wood is allowed (I believe) 50 ft from the water. If a local builder suggested to use PT then there may be some way around this but be careful.
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leebree
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# Posted: 11 Jun 2013 13:20
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We are grandfathered in, so long as we do not change the footprint of the cottage and the porch.
I do know that Quebec allows docks to be made out of treated wood, so I assume footings will be okay as well. But it's certainly worth checking.
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razmichael
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# Posted: 11 Jun 2013 14:09
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Quoting: leebree I do know that Quebec allows docks to be made out of treated wood,
Not in our area (just south of Maniwaki). No treated wood within 50' of the high water mark. Must be local then. That leaves more options for you.
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creeky
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# Posted: 11 Jun 2013 15:20
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yikes. that's a real bag of tricks.  so ideas
1) eastern white cedar is naturally rot resistant (high silica content ... discovered this ruining some planing knives) and probably a fair price around you. in fact it tests better than redwood. and of course you're not putting poison in the ground or close to your family.
2) why don't you cantilever as per the old deck? and then put adjustable posts on pads to hold the cantilever up. you would be able to adjust if needed to level? check those "makeshift steel posts". I'll bet somebody did some thinkin' before they installed them. are they adjustable?
3) how marshy/wet is the soil? I know my lane entrance, 1200 feet from the river, can rise and fall a couple of inches through the winter. but the soil there is very wet.
I would look very carefully at what was done previously. Those old guys often knew a lot about local conditions that doesn't show up in books.
and I'll put in another thumbs up for eastern white cedar. if you can find it locally it's relatively cheap, very long lasting, and your kids can lick it ... and they will. lol
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leebree
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# Posted: 11 Jun 2013 16:27
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Thanks for you thoughts to far!
We are definitely going for local white cedar for the decking, railings and posts (at least the posts above the deck level.). I am hoping to avoid treated wood as much as possible, especially for the parts people walk on and touch. I will be using treated wood for the substructure.
But even the sawmill doesn't recommend burying their white cedar posts...i am not convinced a buried white cedar 6x6 would last too long in these conditions. The soil just in front of the porch does get marshy after rain and after the snow melt.
The temp steel posts currently are not adjustable - also they are completely off kilter - the base is falling over, so they have 'failed' essentially and are not doing the job they were supposed to do. They do look like a temporary hack job.
I am intrigued by your idea of an adjustable steel post on a concrete pad, and supporting the current cantilever. I assume they would have to be adjustable by several (6?) inches for frost movement. Do you know any suitable products? And what size concrete pad would you recommend to minimise movement?
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Rossman
Member
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# Posted: 11 Jun 2013 18:05
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We didn't even dig for our deck in quebec, just put the 4x4" posts on top of those concrete "feet"...nothing has moved in over a decade *shrugs*
We're close to Lake Ontario on the QC side so I know all about restrictions around the waterfronts there...
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leebree
Member
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# Posted: 12 Jun 2013 10:35
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Our main concern is because the porch holds up part of the roof - any movement will impact the roof structure - and the wetness of the soil / proximity to the lake (we are only two feet above water level).
I'm thinking of going with the following system - helical metal posts. It seems well suited for situations like this one. As they drill the posts they know exactly the load bearing capacity, and they guarantee there will be no frost movement.
http://www.technometalpost.com/en/home/
More money than i'd hoped to spend ($170 per post) but at least I know it will be rock solid.
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adakseabee
Member
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# Posted: 12 Jun 2013 15:46
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You could use post protectors in which you could place your posts in the ground that isolates the wooden post from the soil (and moisture) that surrounds the post. Check this website:
http://www.postprotector.com/sizes-prices-literature/index.html
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creeky
Member
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# Posted: 14 Jun 2013 09:17
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those helical posts look cool. thx. i have very "plastic" clay that I'm struggling with so am going to look into those.
btw. in quebec Rona sells Pylex posts for 20 bucks that look very similar but you install yourself.
and larch (tamarack) and black locust posts also do well in soil. Black locust posts are said to last a 100 years (wikipedia). I just cut some locust on my property so I'll try them out and report back 
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razmichael
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# Posted: 14 Jun 2013 09:49
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Quoting: creeky Rona sells Pylex posts for 20 bucks
Also available at Home Depot. Both have the adjustable version which is much cheaper at Home Depot adjustable. I looked at the TechnoPosts for my cabin but went a different path in the end. The Pylex posts look really interesting for decks and such. I suspect they do not go in as easily as the video implies! Pylex also has a "commercial" version designed for a 6x6 post - not adjustable.
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leebree
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# Posted: 17 Jun 2013 23:02
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In the end we went with the Techno posts. I have to say it's a quite brilliant system - the rig is small and very manouverable. They can go in at an angle and then push the post level, which means they only need 3ft vertical clearance - essential in our case, so we didn't have to demo the entire structure before drilling.
The 6x6 plates are adjustable plus or minus a few inches, which makes levelling the beam very easy.
The operator was excellent - drilled five posts in an hour, accurate to within one inch. it ain't cheap...but I think it's worth it in my case, given the dicey conditions of the soil and the proximity to the lake. I also saved a day or two spent digging holes and pouring concrete etc.
Those Pylex posts look pretty interesting (esp the price) although in my case we would not have enough space to turn the screw with a long piece of lumber (the cottage would be in the way, since the porch is only 6 feet wide)
Adakseabee, the plastic post protectors also look interesting also for buried 6x6 posts.
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creeky
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# Posted: 18 Jun 2013 09:38
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leebree the sanity saved with the techno post was worth the price of admission for sure. one day and you're done. that is sweet.
i bought 12 pylex adjustable posts at HD. As Razmichael points out, they're cheaper (by $7) at HD in Quebec than Rona.
I'll report back when I install them. I'm thinking I might rig them to the back of my tractor auger and zip 'em in that way. (insert whistling sound here).
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razmichael
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# Posted: 18 Jun 2013 10:20
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Quoting: creeky I'll report back when I install them
I'm looking forward to the report. I have a couple of projects where these may prove valuable - given the reasonable price.
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