May 2002 Edition

Sagging Floors

We live in an old house that was built in the 1930's. It is a grand old house, but has several problems we would like to fix. One of them is a sagging floor. Do you have any suggestions on how to start?
The first thing I would do is try to find a contractor or carpenter that specializes in older homes. All of the wooden floor structure should be thoroughly inspected for wood decay and insect damage. Wood decay or minor cracks may or may not need attention. "Checking" are cracks that run in the direction of the grain and form when the wood was originally drying out. Most of the time these cracks do not affect the structural stability. You want someone who is experienced, understands the properties of old timber and can evaluate these conditions fairly.
You need to be cautious of contractors who want to do unnecessary repairs. If you have a contractor that you suspect is overreacting, then an independent inspection is advised by an inspector that does not do contracting or refer contractors. Have the inspector mark on the framing the location where repairs are needed and a brief description of the repair.

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Finally, "jacking" is something I personally try to avoid. Wood structures naturally sag over time which involves gradual bending and stretching of the fibers. Sudden jacking can stress these stretched fibers and create problems in other parts of the house such as cracks in the walls and ceilings. Minor jacking may be only necessary to reinforce joists and beams. Often posts or columns are needed to reduce the spans of the joist to reduce the bounce in a floor. If jacking is needed, it should be done very gradually over a period of months.
One source in locating a specialty contractor is to contact the National Association of the Remodeling Industry (NARI) and obtain a list of the their members which includes a brief description of their specialty. Their phone number is 404-766-7179 or

Makeup Air for an Exhaust-Only Ventilation System

I’m building a tight house with above-average attention to air sealing, and I plan to ventilate with a Panasonic exhaust fan running continuously. Will the cracks around windows and doors admit adequate makeup air, or do I need to provide wall vents?
Bill Rock Smith, building consultant and former contractor, responds: Studies have shown that even a tight home usually has enough openings in the building shell to provide makeup air for the base ventilation rate of most homes (45 to 90 cfm).

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Dedicated passive makeup air inlets have been shown to be ineffective, since the fans used for ventilation typically do not generate the high level of negative pressure (10 to 20 pascals) needed to draw outside air through the inlets.
The main concern for your proposed system is not whether the house has enough cracks for makeup air; it is whether the makeup air will be drawn from the wrong locations.
Potentially, an exhaust-only ventilation system can cause backdrafting of open combustion systems (fireplaces, water heaters, furnaces, or boilers), or the entry of soil gases into the home. If you plan to use exhaust-only ventilation, it’s important to install a pre-radon mitigation system and to use only sealed-combustion appliances. Before using any open-combustion systems, a worst-case depressurization test of the house should be performed.

Source: October 2001, Journal of Light Construction

Weight Limits for Ladders

I weigh 230 and my ladder is rated for 225 pounds. Do the listed weight limits for ladders and scaffold planks include a safety factor? If so, how much weight can be added beyond the listed weight until failure occurs?
Alan Kline, president of Lynn Ladder and Scaffolding Co., Lynn, Mass., responds:

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As a general rule of thumb, OSHA requires ladders and scaffold planks to be designed with a 4-to-1 safety factor. That means that under test conditions, they must be able to support four times their weight rating without failing.
As to when any particular model might fail, that depends on many factors. Overloading any ladder or scaffold plank is a violation of OSHA regulations and is not recommended under any circumstances.

Source: October 2001, Journal of Light Construction

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