Post Number: 56
|Posted on Sunday, February 16, 2003 - 02:24 pm: |
SHORT-FORM SPECIFICATIONS - 22
Copyright 2003 by Herman R. Hoyer, PE, FCSI, CCS
In my last Column, No. 21, I promised to revisit my Quality Assurance Section with some important observations of its contents, which we haven't already covered. For this column, I want to cover protection of wood framing and other wood products from moisture--a very important quality assurance requirement.
In this instance, Paragraph F. below, "Protection of Wood," has nothing to do with the short-form mode of specifying. In fact, the exact same language is in my long-form specifications, which is another illustration of the fact that I never leave out anything important from my short-form specifications.
This paragraph has to do with the fact that wood should never be allowed to get wet. The worst thing that can happen to a wood-framed building is for the wood framing and sheathing to be rained on before it is protected by roofing and siding. And then, before the wood framing has a chance to dry out, it is enclosed with exterior and interior finishes, such as exterior stucco and interior gypsum board.
When wet wood is physically confined, as it is when enclosed with exterior and interior finishes, stresses caused by shrinkage during drying cannot be freely released. This causes tensions resulting in checks and twists, splits, cracks, and deformations in the wood. As the wood continues to dry, tensions increase resulting in cracks in the stucco and drywall nails to pop, not to mention wood warped out of plumb and level.
At the Class-Action Suit brought by the homeowners against the Developer of a housing tract in the Westborough District of South San Francisco (60 wood-framed houses stood naked in the heavy rains of 1972-1973.), some homeowners testified to the fact that they were often awakened in the middle of the night by ear-piercing cracking sounds coming from within the walls and ceilings of their homes. Others complained of hearing more subtle ghostly noises, punctuated occasionally by squeaky creaks.
Needless to say, wet wood must be avoided at all costs. Here is my "Protection of Wood" paragraph as it appears in my Quality Assurance Section. You should consider adding this same text to your specifications where wood framing or other wood products are involved.
F.Protection of Wood:
1. Provide protection of all wood materials and products, whether or not installed, including erected and installed wood framing and sheathing, from water and moisture of any kind until completion and acceptance of the Project.
2. The Contractor shall keep informed of weather conditions and forecasts and, where there is a likelihood of rain, shall protect installed and exposed framing and sheathing and stored lumber exposed to the elements with suitable water-repellent covering, such as canvas tarpaulins or polyethylene sheeting.
3. Likewise, millwork and trim, paneling, cabinets, shelving, and other products manufactured from wood shall be kept under cover and dry at the shop until time for delivery. Such materials shall not be delivered to the site until the building is roofed, and the exterior walls are sheathed and protected with building paper as a minimum, the doors and windows are installed and glazed, and there is ample interior storage space for such materials and products. Delivery shall not occur during periods of rain, heavy dew, and fog.
4. Wood materials or products which become wet from rain, dew, fog, or other source will be considered to have moisture damage and will be rejected, requiring replacement by the Contractor with new, dry materials or products at no increase in the Contract Price. Excepted materials: installed exterior wood siding, exterior wood trim, exterior wood doors, and exterior wood windows, after specified treatments, such as exterior wood stain or paint, have been applied.
5. Compensation for wood protection materials and services will be provided on a unit-price basis. Include in the Bid Form and Agreement a unit price for providing the above specified protection, each occurrence. Include as an exhibit to the Owner-Contractor Agtreement.
If your specifications contain a unit-price section, then the following reference may be all that is necessary:
5. Refer to Section 01270, Unit Prices, for compensation provisions.
My next column will be a surprise, since I am not sure yet what the subject will be. But I'm sure it will be provocative.
Post Number: 57
|Posted on Monday, February 17, 2003 - 11:42 am: |
These responses were posted in Topica, which the CSI Newsletter Editors use:
From Jason Popelka in St. Louis, MO (email@example.com)
Mold and mildew are significant liability issues in construction. Moisture
exposure to wood is a major problem not only for swelling and shrinkage, but
for indoor air quality and health issues associated with elevated mold levels
in the environment. Here is another take on the excellent idea to protect
wood against moisture absorption:
"F.Protection of Wood:
1.Provide protection of wood materials and products, whether or not
installed, including erected and installed wood framing and sheathing, from
water and moisture until Substantial Completion of the Project.
2.Keep informed of weather conditions and forecasts. Where there is a
likelihood of rain, protect installed and exposed framing and sheathing, and
stored lumber exposed to the elements with suitable water-repellent,
breathable coverings, such as canvas tarpaulins or Tyvek.
3.Keep millwork, trim, paneling, cabinets, shelving, and other products
manufactured from wood under cover and dry at the shop until time for
delivery. Delay delivery to the site until the building is roofed, the
exterior walls are sheathed and protected with moisture barrier, the doors
and windows are installed and glazed, and there is ample interior storage
space for such materials and products. Do not deliver during periods of
rain, heavy dew, and fog.
4.Wood materials or products which become wet from rain, dew, fog,
condensation, or other source; or which exhibit mold, mildew or
other moisture damage, will be rejected, requiring replacement by the
Contractor with new, dry, undamaged
materials and products at no increase in the Contract Price. Excepted
materials: installed exterior wood siding, exterior wood trim, exterior wood
doors, and exterior wood windows, after specified finish treatments, such as
exterior wood stain or paint, have been applied."
From Phil Kabza (firstname.lastname@example.org)
Herman, I have to comment on your most recent column, which like the rest I
make sure I don't miss.
I worked in the construction trades as a carpenter and builder for 15 years
prior to entering architectural practice and need to take some exception to
several of your comments in the current Quality Assurance discussion
regarding wetting of wood members during construction. Most of the over 50
houses I worked on during that time (all in Michigan) were significantly
wetted while being framed. Once sat open following a disastrous New Year's
ice storm for two months. Rain and snow are a normal part of residential
construction life in many such climates. Bunked lumber and plywood was
sometimes protected, but framing and sheathing, once installed, remained
unprotected. The likelihood of a builder being able to securely tarp an
entire framed house is nill. Nontheless, we seldom if ever had a noticeable
problem with callbacks resulting from nail pops, cracking or shrinkage. We
did not experience mold/mildew problems resulting from rain exposure.
Granted, the crews I worked with didn't scrimp on nailing. Nor did we work in
coastal or high humidity areas where structures would be unlikely to dry out
properly prior to finishing. I expect there are some regions where climate
conditions would combine with rain exposure to cause problems. But there are
many areas where this is unlikely, too. Wood exposed to short duration rain
does not typically become saturated, and can typically dry out in the time
between felting of the roof and finishing of mechanical and electrical
roughins. Herein may be the prime issue: quick installation of insulation and
vapor barriers following wetting of framing would very likely cause the
problems you describe.
Post Number: 6
|Posted on Tuesday, May 17, 2005 - 12:22 pm: |
In the Pacific Northwest, we expect that wood framing and sheathing will be exposed to rain and snow during the course of framing. I agree it is impractical and costly to basically "tent" a wood frame house, but stored rough framing wood material should be protected as described above.
We specify the moisture content of inplace rough carpentry materials not to exceed 19% at "time of covering." Basically, the same moisture content as shipped from the mill.
Some trivia on MC and Mold/Rot:
General Moisture Conditions for Mold/Rot:
0-19% : Immune to fungal growth
19-28%: Fungal growth sustained (no germination)
28-40%: Germination and growth
40-80%: Optimal moisture conditions
Accuracy of Delmhorst meters:
0.5% at MC of 6-12%
1% at MC of 12-20%
2.0% at MC of roughly 20-28%
Inaccurate above roughly 28%
Resistance Type Moisture Meters:
Including varying accuracies of meters, there are correction factors for species and temperatures.
Delmhorst Calibrated to take readings of D Fir at 68F.
Example: Meter reading of 25% for ponderosa pine at 40F is actually MC of about 31%