WOOD FOUNDATION –
Long story short, (concrete) foundation of new house has lookout basement, top of foundation is lower than max flood condition. City is requesting that grade be increased (20″ higher than today) in order to eliminate possibility that water will come over top of foundation if near by storm sewer backs up.
Have considered taking cement siding off, replacing OSB with pressure treated plywood and sealing with ice and weather shield as membrene, and backfilling grade up against house.
I am nervous about having organic material even if it is treated, below grade. I was also thinking about backfilling up against house with gravel, in order to have drain tile effect so water will not pool up against wood. I am somewhat concerened about the durability of ice and weather sheild and have also considered putting some type of flashing to futher protect membrene. House is located in “Chicagoland” – fairly severe winters.
Are there special materails that can be used as membrane or different materials and or techniques that can be used?
Any comments/suggestions would be greatly appreciated!
JJW
Replies
I'm normally not an advocate of wood foundations, but, in your situation, since the situation calls for protection from a potential occasional risk, you might be OK with the PT plywood.
But rather than the the ice and weather shield, you might look into having one of the sprayed on "rubber" membranes applied over the plywood and continuing down onto the concrete.
I have these applied as a regular practice anymore...they're self-healing and go on about 1/8" thick and are not terribly expensive. I recently had a 90' perimeter of a 10' wall done....the applicator had to come 130 miles and the cost was just over $1200.
It doesn't tolerate UV for very long though, so you'd want to cover it with a flashing, where exposed (SS?), and your siding within a few months.
And it would work best if the bottom edge of your PT sheathing could be let in flush with the concrete so the application ends up smooth, without a jog at the seam.
Thanks Notchman, that is a good idea!
I don't think the pt plywood will be flush with foundation?? should be 1 - 1-1/2" ledge of foundation??? Would have to shim it out to make that happen?? Do you think it is worth effort???
What about putting flashing down on seam (roofers - baby tins??) and than having membrane sprayed over??
Appreciate your input..............
JJW
Well, you probably understand why flush would be better, but if that's not a feasable option (and I can understand why it wouldn't be) then you might think about carrying the PT plywood down past the mudsill 2 or 3 inches but bed it to the foundation with a good quality caulking.
I would probably use something like Vulkem 921 poyurethane sealant (most building supplies should have) or a good marine adhesive sealant (any good marine supply that deals with wooden boats should have, or peruse ads in WoodenBoat Magazine), cover the entire mating surface between plywood and concrete, nail it in with a powder-actuated nailer or use tapcon screws and then have the membrane sprayed on.
I recommend the above types of sealants because you'll be joining dissimilar materials, and the sealants I've mentioned maintain a tough, rubbery consistency when cured and also act as adhesives.
If the applicator understands what your needs are, he may be able to ensure that he gets a good coating at the bottom of the plywood sheathing.
Of course you'll probably need to run this by your building authority to get their blessing before you proceed with the expense and the effort.
Good luck and let us know how things turn out!
You know , I have this feeling, things will turn out OK/Good for you on this. Why, you may ask,well I'll tell you, You are not afraid to ask those questions , You will probaly put it all on the table, have a look see, make an informed decision, then do it. Best of luck. Jim J
How confident are you in the City? ie you raising the existing grade. Seems to me someone dropped the ball. Just curious, what would happen if you did nothing? Or, can you "cut" your existing grade down lower, or would that create a swimming hole, sounds interesting, good luck. Jim J
Confidence..............hhmmm.... based on my experience with city, I am confident that similar will occur again with others, just a gut feeling.
You are correct, several did not do their job.
Engineering Firm - they were responsible for placement of structure as per the development plan as filed with the city by developer. They are to respect set back provisions as well as elevations.
City Building Dept - they approved Engineering Firm's mistake on paper, they also had an opportunity to catch when Engineering Firm submitted survey detail of foundation prior to framing.
One possible benefit, I have look out basement, if things had been done per the plan, I would not have had windows in basement, (I am an optiamist)
I am living in house, city has $1,000.00 of bond $$ that they will keep until I get final grade approved. I am confident that I could I could push and get my $$ back, but this does not address my concerns, of which there are two.
If storm sewer backs up to max. flood condition, there is potential for water to come over top of foundation and flood the basement. Max Flood conditions calculations are not precise, there are many variables that have large impact, so there is no accurate way to gage the level of threat.
As big a concern for me is to have adequate slope away from structure, recently we had 4" of rain, sump pump ran every 6 mins, even the day after when it was sunny. It looks like I could cut a swale in back yard and could "eek" out 1% grade to same storm sewer that I am concerned about , who knows what the "as-built" could be. Yard is small, swale will look stupid and will make it harder for my wife to mow grass (and she says I am inconsiderit).
Plan is to live in house for next 30 years, it is custom home that we planned. I am very interested in coming up with plan provides a reliable solution. I am not really interested in getting all "lawered" up, would just prefer to fix my problem and move on.
JJW