Renovation & Design

Renovation & Design

Extruded polystyrene insulation a good bet in basement

Question: We want to refinish our old 1970s basement, take out the panelling, and install drywall.

We noticed there was vapour barrier behind the insulation, not in front. However, the insulation is kraft paper faced. Is this OK? Also, we noticed fibreglass insulation in the joist spaces without vapour barrier. We saw an article in the Free Press about this.

Is it OK to remove the insulation, install rigid foam board, seal it with a can of spray foam, and then add Roxul in front, which should act as the fire barrier?

If we do that, I understand we don’t need a polyethylene vapour barrier, as the rigid foam acts as the air/vapour barrier.

Thanks, Gordo.

Answer: Insulating the inside of a foundation wall must incorporate a good air/vapour barrier, to prevent condensation and moisture issues, but the type and location may be up for debate. Using rigid extruded polystyrene may work, as long as it is thick enough, well sealed, and the local building authorities approve of leaving off the poly on the warm side of the wall assembly.

Building science, as will all science, is constantly evolving. As we gain new knowledge, older theories and methods become replaced with newer ones. This also applies to the construction of our buildings. Because of this, the National Building Code (NBC) is revised approximately twice a decade. Also, it may take some time for contractors to change habits that they have been using for a long time. Methods that have been used for decades may suddenly require replacement with more modern ones, and be required by building officials in various jurisdictions. Because of this, you should consult with the building officials in your area, when you apply for the building permit to upgrade your basement, whether your proposed insulation method is OK.

The conventional way of insulating the inside of a house foundation wall, to retain heat and make the basement more comfortable, is to use fibreglass batts and a 6MIL polyethylene air/vapour barrier. Because the fibreglass is not very restrictive to air movement, and warm air can pass through, it must be sealed on the warm side to prevent this from occurring. If not, the warm air will slowly move through the insulation, losing its heat energy as it does, and will often condense inside the batts, or on the foundation wall. Since the insulation prevents heat from escaping the basement through the foundation, the inside of the concrete wall will be cold. In the winter, that temperature may be below freezing, which can cause the condensation to freeze. As soon as the weather warms in spring, this frost will melt, wetting the insulation further, or even leak out the bottom of the wall assembly. This is even more likely to occur on the area at the top of the wall, where you have stated the current batts are not even covered with polyethylene sheathing.

Since there has been much more wall assembly research in the last couple of decades, it has been determined that a better location for the air/vapour barrier may be inside the wall assembly, or on the outside of the building, not the inside. Those methods make a larger portion of the wall cavity warmer, further preventing condensation. For your purposes, that could be accomplished by installing rigid foam insulation first, before batts on the warmer side of the wall cavity. That would prevent warm air from contacting the cold concrete foundation walls, and would be more cost-effective than filling the entire cavity with foam. The key would be to use a minimum of two-inch-thick extruded polystyrene, which would be required to achieve a good air barrier. The foam should also be continuous, so the wall studs should be installed inside the sheathing, to prevent air gaps behind the studs, which can lead to condensation and mould growth. Sealing any gaps between sheets, and around any protrusions, with caulking or spray foam from a can will complete a good air sealing job. Adding a layer of batt insulation on the warm side of this will allow you to bring the wall assembly up to current thermal standards, with lower cost than using the foam sheathing alone.

Depending on the thickness of the wall, the air/vapour properties of the foam sheathing should be sufficient to leave off the poly layer, but that will largely depend on the approval of the local building officials. They may be old school in their thinking, and still require 6MIL poly on the inside of the studs. This use of a double air/vapour barrier may not provide much advantage, but should not be a major detraction, either. If the building officials stubbornly insist upon it, there should be little chance of causing moisture damage inside the wall assembly, as many people would worry about. This is because the polystyrene insulation will prevent any warm air leaking through the poly from cooling sufficiently to condense. It will not be able to leak through to the freezing cold foundation wall, so any moisture within will stay in vapour form, inside the warmer wall cavity. This was thought to be a major potential problem when exterior foam insulation use became more common, but more recent testing and practical experience has shown that it does not pose a moisture damage threat to the wall assembly.

The inside batt insulation, whether fibreglass or mineral fibre is used, will not normally be a sufficient barrier to protect the foam insulation in case of fire. Since you are planning on putting drywall up in place of the older panelling, that will do the job. Standard half inch thick drywall should be acceptable, in many areas, but check with the building officials first to ensure they don’t require five eights inch thick fireguard drywall for full protection.

Using your method of extruded polystyrene insulation as a first layer to insulate your basement walls is a good idea, if it is continuous and thick enough. Ensuring this will meet the approval of the local building officials should also be done, before finalizing your plans.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

Ari Marantz
August 21

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Renovation & Design

Fence replacement likely better idea than repair

Question: I have a PVC fence that is over 20 years old. The fence is sagging in spots and I am worried about the integrity of the fence. Last winter one of the panels had a problem. The bottom rail somehow dropped and almost all the pickets in that panel fell out. That section of the fence is behind the garage and I was unaware that it happened. Fortunately, someone walking behind the fence let me know what happened. I just happened to have a sheet of press board in my garage, so that was my fence until the weather warmed up and it could be fixed. In the spring, I contacted a few vinyl companies to see if they could advise me what to do, especially with the sagging issue. Two companies didn’t come out, as they said this fence is not their product. They did give me a quote on replacing the fence. One of the companies said it probably is a fence from Sears, but that sure doesn’t help. I don’t know who took over maintenance after Sears closed.

I would like to know whether I should replace the fence or if it can be shored up so the sag doesn’t worsen. Because this issue is not house related, you may not be able to help, but you may be able to direct me to someone who may be of some help.

Thank you, KLT.

Answer: Replacing portions of outdated manufactured fencing may not be practical, due to the difficulty in finding similar or identical components. Budgeting for a complete replacement is likely the only good solution for a fence of that age.

There are many types of materials used for residential fencing, still mostly wood or composite wood products, but newer materials have been available for a while. These range from vinyl coated chain-link metal fencing, which has been around for decades, to various types of plastics. The PVC and other plastic fencing materials are generally newer, but various lattice and trellis materials are becoming more popular. The benefit of a metal or plastic fence is the obvious lack of maintenance required, compared with various types of wood.

Most older wooden residential fences were made of lower cost materials, like spruce or pine. These types of softwoods were economical and easy to work with, but had very little moisture or UV resistance. For this reason, they had to be stained or painted ever five years, or so, to prevent premature damage. This was a laborious chore, especially if solid colour paints were used. Often, older paint would partially flake off and have to be scraped, sanded, and primed prior to recoating. Still, these boards had limited life expectancy, around 20 years, even with good maintenance and regular new finish applications.

A more costly, but far superior, option was to use cedar for fencing, which has natural resistance to rot. That type of wood was often used only for posts, to prevent rotting in or above the soil. When it was used for the entire fence, rails and pickets in addition to the posts, the longevity of the increased to approximately 25 years. The cedar did not have to be painted or finished, which severely limited the maintenance required. The only downside of using unfinished cedar is that the UV rays from the sun would turn the wood grey. When it was nearing the end of its life, the boards would get even darker in colour and be almost black when rot had infested the fencing.

Some homeowners like the weathered grey look of cedar, and many later composites copied the colour and texture, to simulate a more authentic appearance. Many of these types of materials use wood byproducts, like sawdust or shavings, mixed with plastics and binders to further emulate weathered wood. But unlike wood, these rarely have to be finished and have a longer life expectancy. This type of product is more costly and was generally not used for fencing, but more for decking and other areas where wear and tear on wood surfaces is more pronounced.

In the late 20th century, a process to imbed preservative deep into wood was developed and became known as pressure treated wood. This was done by soaking lower cost softwoods in a preservative bath and driving the liquid deeper into the core by pressurizing the process. In the highest quality method, preserved wood foundation or PWF, the wood is normally incised with small crevices to get the preservative even deeper below the surface. This process was so effective that some of the preserved wood, normally pine, would last up to 40 years, even buried below grade. Later advances added a cedar-coloured coating above the normally green-coloured preservative, which is still very popular for fencing and decking.

Regardless of the advances to wood fencing materials, they eventually rot and need replacement. Vinyl (PVC) fencing, which has been in regular use for a few decades, gained some popularity around the turn of the century. The main problem was the much higher cost of production. While vinyl has a longer life expectancy, it also had to be constructed with more measures to counter much higher expansion and contraction due to temperature changes. This could be why the section of your fence failed, and modifications to allow for the movement may be the only way to save the fence. Otherwise, it is likely impossible to find similar materials, after two decades. Replacing the damaged section and the adjacent ones with pressure treated fencing, or the entire fence, may be the only good solution for the long term.

Trying to replace 20-year-old warped or damaged vinyl fencing materials may be futile, due to the limited production of this costly material. Replacing the damaged sections, or the entire fence, with more popular and less costly treated wood fencing materials may yield a more fruitful outcome.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

Ari Marantz
August 14

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