Roof Issue Lesson

[jkogel]

Originally Posted by Ed Fako

Well, without being able to count the shingle tabs for width, it looks like 24" O.C. rafters.

My guess from seeing similar roofs is the rafter spacing is too wide in addition to the decking thickness being either a cheap 3-ply cdx or a 3/8" cdx.

The improper ventilation just compounded the deflection by steaming away the glues that bond the plies together.

Ed

That would be a good guess, 3/8" being cheap. Too bad for the tenants of this complex, for a saving by the builders of a couple of hundred bucks. Building inspection from ground level, no doubt.
That's the morning sun making the pattern standout. A good picture for the roofing gallery.

[Brian A. MacNeish]

Originally Posted by mcyr

This may help explain somewhat;

http://www.osbguide.com/pdfs/ShingleRidging.pdf
From the above guide:

3. Ventilation

Recent increases in insulation requirements and energy efficient

building design have placed increased demands on ventilation of the
space below the roof structure or attic. This space may collect
significant amounts of moisture vapour from the drying out and
curing of building materials as well as moisture vapour from the living
space, due to cooking, washing, showers, and humidification
equipment, which escapes to the attic through improperly sealed
openings in the vapour barrier. This moisture vapour will affect all
wooden roof components causing some movement.

My comments:

With the knowledge we've had access to over the past 40-45 years, in new houses, it is a travisty that we still have to deal with moisture in attics. The airsealing techniques are widespread and freely available for those who wish to learn. Why are we letting our attics to be the receptor of moisture from our mistakes? As the section says "improperly sealed openings in the vapour barrier"

True storey:

In the late 1980's, we (had an engineer partner then) found that the ventilation rates being specified for HRV's were leading to severe overdrying of houses in their first winters!! Complaints of shocks, nosebleeds, chapped lips, cracks developing in shrinking hardwood floors. We started putting in smaller CFM HRV's but got called in the R2000 program as we didn't meet the still current but original standards.

In 3 of the homes, the air exchange rates per/person by the R2000 standard would have approached the ASHRAE 62 requirements for "SMOKING LOUNGES AND BARS (while occupied)" of 60 cfm/person, yet no one in the houses smoked and they were to be ventilated 24 hours/day continually at rates of 45-55 cfm/person.(how's that, Marcel??) I fought the program to the point of being threatened with legal action by one of the R2000 homeowners since he hadn't received his R2000 "certificate" due to the "too small HRV". In the end, all 3 homes received "special certification"; the program has reduced the ventilation requirements 3 more times without problems!!!

The homeowner who threathened to sue had his house built during a quite wet and damp fall from Sept to move in around Dec 15. The house was hand plastered with thincoat veneer. So all and all, it should have been full of moisture......yes??? The owner called me near the end of January about the house feeling a bit dry. Spoke to him about the unit and that it had an extra low speed installed by the manufacturer (VanEe) for just this purpose......told him he should try it and watch the house moisture levels (since this was the first period of drying for the house....be careful and watch!) Never heard a peep from him (moisture and indoor air quality must have been OK!!) until the R2000 certificate issue came up. (by the way, this episode occurred in 1989)

Point of the storey: Even with wet houses from new building materials, good construction airsealing and ventilation practices stop moisture movement to attics and dry out homes in a couple of months, not the 18 months that we were familiar with in the past. If you have excess moisture in the attic of your new home, it's improperly built and not a roof/attic ventilation problem!!


M

arcel

My 2 cents again!!

[Christopher Currins]

That was my observation as soon as I saw the 2nd photo. I've seen too many of those...mainly on pre-fabs built in the late 70's and early 80's.

[Barry Adair]

Originally Posted by Ed Fako

Sorry Barry,

That remark was in no way intended to diminish my appreciation for the knowledge and fact finding capabilities of many many other posters. It was more of an affirmation about Marcels working background, which seems to have a deep root in roofing techniques.

If I came off the wrong way, I will personally write your customer testimonial letters for you.

That other, more recent photo posted, looks like deeply sumped decking deflection, by the way.

Ed

Ed,

How's your penmanship?

[Ed Fako]

Originally Posted by badair

Ed,

How's your penmanship?

I guess I need to clarify.

I would have to have my secretary hand write you those testimonial letters.

I have to print or type for it to be legible.

Ed

[Robert M. Delre]

you are correct!

[Robert M. Delre]

I would bet that if your inspected the edge of the sheathing it would be 3/8". Many home in the 70's (primarily... the larger builders such as Ryan, Toll Brothers ect.) used 3/8" roof sheathing for a period of time.