Rotted rafters: repair or replace?

If the latter, prepare to shell out big bucks

By Inman News Feed
Add Comment Add Comment | Comments: 0 | Posted Jun. 10, 2009

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If the latter, prepare to shell out big bucks

Bill and Kevin Burnett
Inman News

Q: I have a house built in the late 1970s that has large beams exposed beyond the roofline. After more than 30 years of neglect and exposure there is a good deal of dry rot in them. I think I should have them repaired or replaced.

Is it something I can do, which, considering my lack of construction skills, I seriously doubt, or should I hire a contractor to do the work? Will it be really expensive? Once it is done, how do I keep it from happening again?

A: The bad news is you're right. The exposed beams should be repaired or replaced. The good news is that there's no hurry. The roof is not going to collapse, nor is the house going to fall down.

Depending on the extent of the damage, repair is a possibility. But it's more likely you're looking at replacement. Replacement will be expensive, repair not so much.

The problem is probably worse than you know. Experience tells us that the dry rot you can see in the rafters is only the tip of the iceberg. More likely than not, rot extends well into the beam. Worse yet, most of the rot is probably hidden where the beam meets the roof sheeting. The sheeting is probably rotted too.

Rotten rafters are usually the sign of a failed roof. The 1970s architectural style you mention usually has a low-sloped roof. The roofing material is most often tar and gravel. A leak develops in the roof membrane, then water penetrates the sheeting and runs down the joint of the sheeting and the beam. If the leak is not repaired and moisture is present over long periods of time, both the sheeting and the beam rot.

To get an idea of the extent of the damage, do a little probing with a screwdriver. Get up on a ladder and poke the rotten areas you can see. The screwdriver will penetrate the rotted wood easily. Probe along the beam working in toward the walls of the house until you find that the screwdriver will not penetrate.

Pay particular attention to the joint where the beam meets the sheeting. If you're lucky, the dry rot will be in small areas of the beam. If that's the case, repair is possible. Better yet, you can do it yourself and the cost will be minimal.

Begin by digging all of the rotten wood out of the beam. Once all the punky material is out, treat the inside of the hole with a wood preservative formulated to inhibit rot. Allow it to dry.

Next, prime the inside of the hole with a good oil-based primer and allow it to dry thoroughly. Finally, fill the void with the automotive filler Bondo. Sand the patch smooth, prime and paint.

If you're unlucky and the beams need replacement, we suggest you contact a reputable termite company to come to do an inspection and give you a written report and an estimate for the work. An experienced termite inspector can make a highly educated guess as to the extent of the damage.

To find a reputable company, check with a real estate agent or two. Because they work with termite companies regularly, they have a line on the good ones. With report in hand, get other estimates for the job and go with the licensed tradesman of your choice.

It is not a job for a do-it-yourselfer, unless you're a skilled carpenter. If the roof sheeting is damaged from a leak and the roof is close to needing replacement, it might make sense to do the rafter repair and the roof at the same time.

Finally, the way to prevent future damage is to make sure the rafters have a solid protective coat of paint or stain and that the roof, including the flashing, is in good repair.

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