I was thinking about building a cottage on a lot that’s one big slap of granite rock, can I build right on top or do I have to do something else?
A:
As long as you don’t require a full basement then you can construct your cottage right on top of the granite rock. The granite must be stable, it cannot be flaking or crumbling away. If everything is solid and secure then you can set the concrete walls or concrete footings right on top of the rock.
If the lot that you are thinking about building your cottage on is waterfront then chances are that the rock will be slopping towards the water naturally. This means that the foundation walls of the cottage will be shorter at the road side of the cottage and higher at the water side. This is important because if you want any kind of basement then you are going to have to fill and level with stone the basement area before you pour the concrete slab on top.
Depending on how steep the slope is running to the water you might end up with the road side part of the basement that will be little more than a crawl space and the water side of the basement being full height.
Before you fill and level the basement with stone and pour the concrete slab for the basement floor there should be an effort made to remove all organic material from the face or the crevices in the rock. Even on granite rock plants will find a spot to grow, efforts should be made to remove all of it so that there is no problem at a later date with your concrete floor cracking.
Some thought should be made towards the drainage of the basement as the water will naturally run down hill to the lake but with it being granite the water will not penetrate into the surface, it will run on top of the rock and gain momentum as it falls down the hill. Water should be diverted around or away from the cottage as much as possible.
The thing that will make it building a cottage or home expensive or cumbersome on granite is if you decide that you want a full basement, a full basement that is the same height all the way across the home. Wanting this will require your builder to blast the rock to create the hole for your basement walls. That though is an entirely different question and also entirely different cost structure.
Your footings for your cottage will be anchored usually to the concrete with rebar that is drilled into the rock, This rebar will be then embedded in the concrete footings, and this will hold your foundation to the granite.
Once you have secured your foundation to the granite then there isn’t much difference for the rest of the build then building on overburden. You should have little to no problems constructing your home.
Rob Abbott
Village Builders Inc.
Would love to hear from you. We just bought a cottage in muskoka that has the exact basement you describe here. Full height by lake and smaller by granite. The problem we are having is water running over the granite, the granite sweating and causing increased humidity and mold (as I'm learning granite is 5 months behind outdoor temperature) thus causing condensation. I have huge mold problems on main level of my cottage. My neighbour told me to cover granite with plastic sheets so it sweats to the floor drain. We have done this and added a dehumidifier..seems to be helping. Is this a good idea though? There are only 4 brick sIze air openings to outside no windows to open to help vent. Just door. Would installing a furnace/dehumidifier help?
ReplyDeleteIf you want you can email me at robabbott@villagebuilders.ca and we can talk some more, I can also help deal with the problems that you are having at our cottage.
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