Foundations are complicated. After back filling, it is too late to make changes so getting it right the first time is a given. Therefore having a detailed plan makes sense. The air intake pipes require some attention to detail to ensure they function properly. As warm summer air enters the pipes and begins to cool, humidity will decrease through condensation on the pipe walls. Perforated drain pipes will allow that moisture to drain as long as the material surrounding the pipe can transport bulk moisture. Compacted earth has little drainage capacity so surrounding the pipes with a material that can pack around the pipes in order to make good thermal contact but yet be able to soak up and transport the moisture draining from the pipe perforations is necessary. Class A gravel provides a good medium to achieve this. It will pack around the pipes but allow moisture to migrate. My site is pretty confined at this point and it would be difficult for an excavator to get around so a shovel and a wheel barrow are about as technological as it gets when it comes to moving gravel. It is a pretty monotonous job but I like to convince myself that I do some of my best problem solving while shovelling gravel! Must be a coping mechanism I guess. This being said, I definitely sleep well after moving 9 tons of gravel by hand! The gravel should be sloped since the wing insulation will be installed on top of the footing and out over the gravel below containing the air intake pipes. The slope will provide drainage once the 6 mil poly is installed on top of the wing insulation. I extended the gravel out a little more than 4' beyond the footing. I found that using a landscaping rake works best for getting a flat surface for installation of the foam.
How far should the wing insulation extended beyond the foundation? It is kind of hard to say exactly. The only document that I have found is about insulating frost protected shallow foundations (FPSFs) for unheated buildings. An unheated building is considered to be a structure where temperature inside is maintained at 5 C in winter. For unheated buildings experts recommend that you determine the Air-Freezing index and Mean Annual Temperature first. For St. John's this equates to about 650 Celsius.days (1200 F.days) and a mean annual temperature of 5 C (41 F). The design guide recommends 40" wing insulation around the perimeter of the building at an R-value of around R-6.5 if buried under 10" of soil. There will be about 14" of soil at the front of the building so 4' will work fine at R-8. However at the back the soil will be about 4' deep. The recommendation is to decrease the wing insulation width by 1" for every inch of soil beyond 10". Therefore the wing insulation would only be about 10" wide and just cover the top of the footer. Since I wish to create a thermal bubble under the greenhouse by feeding heat from the greenhouse under ground, I am going to extend the R-8 insulation to 4' all the way around the structure.
In order to prevent water that seeps into the ground from stripping the heat being pumped by the GAHT, it is important to divert water away from the structure. Passive annual heat storage methods recommend installing some sort of vapor barrier material that can divert this water to the perimeter drain. I decided that a 6 mil poly attached to the foundation which extends out beyond the wing insulation could easily divert water towards the perimeter drain. Blueskin is a great way to stick vapour barrier to a foundation, and it is easy to work with when you have 2 people. I joined pieces of the vapor barrier with Stego Tape. Luckily I completed this work just before it rained. The next day I could see that the poly water diversion was working well. The material under the vapor barrier was dry while the area beyond the vapor barrier was substantially wet. So that the material around the foundation doesn't get saturated with water while seeping towards the perimeter drain, I am placing about 2" of class A gravel ontop of the vapor barrier to act as a capillary break. This was covered covered with landscape fabric so that the gravel doesn't get clogged with dirt during back filling.
Jason Wade did my excavation work. I have hired him three summers in a row now and I am pleased with his work. I trust his judgement and often just let him make the decisions after I point out what needs to be done. Overall I am pleased with how the project has come together. I enjoy all the planning and starting a foundation but by the time the foundation work draws to an end I am glad to see it done and buried so I can get on with the framing!
How far should the wing insulation extended beyond the foundation? It is kind of hard to say exactly. The only document that I have found is about insulating frost protected shallow foundations (FPSFs) for unheated buildings. An unheated building is considered to be a structure where temperature inside is maintained at 5 C in winter. For unheated buildings experts recommend that you determine the Air-Freezing index and Mean Annual Temperature first. For St. John's this equates to about 650 Celsius.days (1200 F.days) and a mean annual temperature of 5 C (41 F). The design guide recommends 40" wing insulation around the perimeter of the building at an R-value of around R-6.5 if buried under 10" of soil. There will be about 14" of soil at the front of the building so 4' will work fine at R-8. However at the back the soil will be about 4' deep. The recommendation is to decrease the wing insulation width by 1" for every inch of soil beyond 10". Therefore the wing insulation would only be about 10" wide and just cover the top of the footer. Since I wish to create a thermal bubble under the greenhouse by feeding heat from the greenhouse under ground, I am going to extend the R-8 insulation to 4' all the way around the structure.
In order to prevent water that seeps into the ground from stripping the heat being pumped by the GAHT, it is important to divert water away from the structure. Passive annual heat storage methods recommend installing some sort of vapor barrier material that can divert this water to the perimeter drain. I decided that a 6 mil poly attached to the foundation which extends out beyond the wing insulation could easily divert water towards the perimeter drain. Blueskin is a great way to stick vapour barrier to a foundation, and it is easy to work with when you have 2 people. I joined pieces of the vapor barrier with Stego Tape. Luckily I completed this work just before it rained. The next day I could see that the poly water diversion was working well. The material under the vapor barrier was dry while the area beyond the vapor barrier was substantially wet. So that the material around the foundation doesn't get saturated with water while seeping towards the perimeter drain, I am placing about 2" of class A gravel ontop of the vapor barrier to act as a capillary break. This was covered covered with landscape fabric so that the gravel doesn't get clogged with dirt during back filling.
Jason Wade did my excavation work. I have hired him three summers in a row now and I am pleased with his work. I trust his judgement and often just let him make the decisions after I point out what needs to be done. Overall I am pleased with how the project has come together. I enjoy all the planning and starting a foundation but by the time the foundation work draws to an end I am glad to see it done and buried so I can get on with the framing!
Picture 1. Air intake covered in road gravel. The perimeter was sloped so the wing insulation would slope down from the structure.
Picture 2. Gravel covered in R8 wing insulation. It was temporarily weighed down with rocks to keep the sheets of insulation from blowing away!
Picture 3. The 30 Amp electrical wire running to the house.
Picture 4. The vapour barrier installed up the foundation wall and down across the wing insulation. The edge of the vapour barrier will divert water into the previously dug perimeter drain.
Picture 5. Foundation insulation was installed using foam glue and clamped to the foundation for about 20 mins. The vapour barrier on the wing insulation was first backfilled with road gravel to permit drainage and then covered in landscape fabric to prevent the gravel from being clogged with mud.
Picture 6. Backfilling mostly complete. Luckily there were lots of large rocks uncovered during excavation that could be used to create a retaining wall during backfilling.
Picture 7. A sneak peak of the current status of the project. Framing has started!
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