Home Improvement--General/Icy windows


Hi Tom, Merry Christmas! since you are an architect, i thought you would be able to share your thoughts. We live in Calgary, today is -26 C (-15 F), has been in this range for the past several days. We have 2 furnaces, one for the basement and ground level, the other for the bedrooms upstairs. Each furnace has a humidifier, the hygrometer in the bedrooms upstairs shows 30% at 20C (indoors). The house is 2000 vintage and is a California show home, which we bought this summer. The windows frost up big time, other than replacing windows, what is the best way to control this. Is there likely mould inside the windows, because i suspect this has been going on for years
thanks in advance for your response


Happy Holiday Tom.

Frost on windows is caused by higher humidity warm air hitting a cold surface that drops the water to the dew point, where the water turns back to liquid form (water), and if cold enough continues to solid form (ice).

The ways to stop this are:
1) to raise the temperature of the glass. It has been a HVAC practice in the past to place heat supplies to rise past or blow onto windows to heat the surface first and to counteract drafts and condensation.
2) to lower the interior humidity. Humidity comes from humans, plants, cooking, bathing and your humidifiers.

Based on your information and question - insulated drapes, blinds, shutters and/or storm windows would act to buffer the temperature change at the glass and eliminate or reduce condensation.

There is a plastic product out that can be taped around windows and with a hair dryer heated to make it taut and clear. It is installed inside and acts as a permanent, until torn out, vapor barrier between the room air and the glass.

As far as mold is concerned, the same dew point principal applies to your walls, floor and ceiling and any crack around ductwork. Generally speaking different molds have different humidity and food requirements. Provided moisture and a food source mold will grow. Mold spores are in the air regardless of the appearance of mold on surfaces. To my knowledge the spores are what cause some persons health problems and it only those with a mold sensitivity that suffer from the presence of mold.

Disregarding mold, having repeated wetting of wood building materials can attract wood eating insects and wood rot. Without taking the building apart to see how it was built I do not know of a way to determine the presence of water in the structure until water damage comes to the surface. At that point tearing out enough material to locate the cause can speak volumes about the rest of the structure.

For a short horror story click on water damage.

Home Improvement--General

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Thomas Buford


Licensed Architect in Virginia since 1984.
New Homes, Additions, Alterations, Outbuildings, Failure Forensics;
Small Construction Projects; Remediation and Repair



Architectural design, planning, construction and repair.
Schematic Design
objectives statement
space planning
feasibility study
structural, mechanical, plumbing
and electrical system integration
Permit Drawings
Construction Drawings
Contract Documents
Construction Administration
construction management
pre-qualification of bidders
general and/or sub contracting
construction progress and
construction contract review and interpretation
pay request certification
Construction failure diagnostics
water intrusion
structural failures, ...

Due to life safety concerns regarding some aspects of construction I may not be able to help with all questions.
I do not answer structural specification questions without a site visit.

Arlington Journal

5 year Bachelor of Architecture from
Virginia Polytechnic Institute and State University (VPI-SU)

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