Proper sealing key to basement insulation

Hey there, time traveller!
This article was published 14/04/2002 (8596 days ago), so information in it may no longer be current.

Question — I always look forward to your column in Sunday’s Free Press and I have a question for you. My gas meter is located inside my home in the Northeast corner. I have framed, insulated and drywalled the basement up to and around the gas meter. However, the last time I did a meter reading, I noticed an accumulation of frost behind the meter on the bare concrete wall. Is this something to be concerned about? My concern is when spring and summer roll around the frost will melt, leaving moisture and the potential of rot or mildew in behind the framing. Will the frost buildup affect the gas meter or gas line piping?

Your comments or suggestions are greatly appreciated.

— Barry Spencer, e-mail.

Answer — Insulating interior concrete basement foundation walls is an excellent way to improve the energy efficiency of a home, but must be properly sealed to prevent problems like that encountered by Mr. Spencer. A properly installed polyethylene air-vapour retarder is essential to preventing condensation. This plastic barrier is difficult to seal around protrusions through the foundation wall, such as gas meters, as well as around floor joists and other uneven areas. The use of acoustical sealant or other flexible caulking and blow-in foam insulations can be helpful in tricky areas.

The condensation behind the gas meter in question is likely due to the presence of the bare concrete wall behind in addition to the metal gas line penetrating the foundation wall. Since insulating the basement walls, Mr. Spencer has limited the amount of exposed, cold bare concrete wall. The warm, moist air in the basement will be attracted to this small area and will condense when it hits the cold wall. If there is cold air infiltration around the pipe, this condensation may freeze and frost will build up. He is accurate in assuming that this will melt in the spring, and drip down the wall. This will often be minimal, but may cause moisture damage and mould over an extended number of years.

The first area to inspect is the area around the gas pipe on the exterior of the house where it passes through the foundation wall. There may be a gap or space that needs to be sealed. This can often be done with an exterior-grade caulking or blow-in foam insulation, if the opening is larger. Both of these compounds are readily available at home centres and many retail stores. They are easily installed and can be painted to match existing finishes, when cured. Closing this gap will be the first step in preventing frost by stopping cold air intrusion into the basement.

The next area to address is the bare wall behind the meter. If there is a gap around the gas pipe in this area, it may be sealed with the same methods used outside. Even after this is accomplished, there still may be the chance of frost accumulation on the exposed wall and the transfer of cold through the metal piping. It is normally advisable to leave a space around the meter, when framing, to allow for removal and replacement of the meter, if necessary. If this is done, there may be a small gap between the wall and the meter and a space of bare concrete around the area. This space could be covered with a layer of rigid foam insulation that could be slipped behind the meter. This insulation could be glued to the concrete wall with adhesive designed specifically for this use. The insulation should be sealed to the existing poly air-vapour barrier of the surrounding walls and caulked around the gas pipes. The foam will provide a partial vapour barrier on its own, and if thick enough, will prevent the problematic condensation.

If the meter is too close to the wall to allow installation of rigid foam, or access is limited, there is another alternative, although it is less desirable. Expanding blow-in foam, available in aerosol cans, may be shot in behind and around the meter to insulate and seal the area. This foam is moisture resistant and will insulate and seal the cold concrete wall. The downside to this product is that installation is messy and difficult to control and the material if very hard to remove if it gets in undesired areas. It will stick to almost anything including the gas meter, and the gas utility may not be pleased if this covers the meter or prevent easy access and reading. A call to Centra Gas for their authorization would be advisable before foaming.

Ari Marantz is owner/inspector of Trained Eye Home Inspection Ltd. and is the P. R. Rep. for the Canadian Association of Home Inspectors- Manitoba (www.cahi.mb.ca). Questions can be e-mailed 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.

trainedeye@iname.com