QUESTION: About 10 years ago, a sunroom was attached to the back of my house, with access from the back door. The floor level of the room is about 12 inches from ground level. The floor was insulated with yellow fibreglass batts. The walls and ceiling have been finished and now we want to install vinyl flooring to make it complete. Before we install flooring, I was wondering if we should be changing the insulation to something rigid or if the fibreglass is fine. My concern is with the fibreglass getting wet and causing problems in years to come. If we need to change the insulation, how would we go about doing it, as we can't work from underneath?
Thanks,
Diane Nichol, email
ANSWER: Fibreglass batt insulation will not rot or deteriorate when it gets damp, as it can hold a considerable amount of moisture, due to the large amount of airspace between the strands. But if the batts remain wet for long periods of time, it can accelerate rot of the floor joists.
The first thing to consider is whether the sunroom is to be heated or not. If you don't plan to use the room in the winter, the insulation under the floor should provide little concern, or benefit. If the building is not heated and the underside of the floor joists is open to the air year-round, there should be little chance of the insulation becoming wet from condensation.
There is some possibility it will get wet from contact with melting snow that blows under the area in the winter, but that should easily be controlled. Removing excess snow around the sunroom in the early spring or putting up temporary skirting to prevent blowing snow may eliminate that issue. Be sure to remove the skirting after the snow melt to allow the damp soil under the area to dry. In that case, leaving the batts where they are should not create a problem, except to provide a possible haven for mice or insects.
If the sunroom is to be used in the colder months and heaters are installed to make it habitable, then heating the room above the crawlspace may cause the flooring to become considerably warmer than the outside air. Insulating this floor with fibreglass batts will not prevent warm-air loss to the underside of the sheathing, but will slow it down, unless a really well-sealed air/vapour barrier was installed. This warm air may condense inside the insulation, as it cools, creating a moisture and frost problem when the weather warms.
This may or not be a big issue, depending on the amount of heating and the air leakage in the rest of the addition, but could cause premature rot in the floor joists and sheathing, if they are not pressure-treated. If this matches your usage, replacement with foam insulation may be warranted.
Another item to address is the need for floor insulation, in the first place. Whether you heat the addition or not, insulation in between the floor joists will do little to make the room more comfortable and will not prevent much heat loss. Because of the fact that warm air rises, even a well-insulated floor may be uncomfortably cold in a situation like yours. This cannot be solved simply by adding or changing the floor insulation.
The solution to this is to remove the insulation from the underside of the floor and replace it with well-insulated skirting around the perimeter of the crawlspace. After that is done and a good air/vapour barrier is installed over the insulation and soil at the bottom of the crawlspace, adding heat to the crawlspace will complete the job. In that situation, heating the crawlspace will warm the underside of the floor sheathing and the insulated skirt will prevent cold-air infiltration, which would make the floor feel even colder in your current configuration.
It may indeed be difficult to complete any work under the floor due to the limited space available. Because you have not installed floor covering in this area, it may be possible to pull up some sections of floor sheathing to allow access to the crawlspace and the dirt floor below. This will be easier if the sheathing was screwed down, as the screws may be backed out using a power drill or drywall gun. Once the underside is exposed, much of the insulation and air-sealing work could be completed after the perimeter skirting is installed from the exterior.
I would suggest leaving the floor alone unless you plan to heat the building for cold weather use. In that case, a complete renovation of the underside, including insulated skirting and heat, will be the way to go.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the president of the Canadian Association of Home & Property Inspectors -- Manitoba (www.cahpi.mb.ca). Questions can be emailed or sent to: Ask The Inspector, P.O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca
trainedeye@iname.com
