Yes, rain and snow during the construction of the house might decrease
the quality of the finished house in several ways. However, there are
ways of avoiding these problems.
My home country, Norway, is a country with lots of rain and snow, and
most residental houses are built with wood. I checked your question
with Norsk Treteknisk Institutt (Norwegian Institute of Wood
Technology), which is the research centre for the Norwegian sawmill
and timber industry. They pointed me to two online fact sheet that
describe your problem. These are in Norwegian only, but I've
translated the key information below.
What are the consequences of incorrect moisture levels?
Wood that is exposed to certain moisture/temperature levels for some
time will start to rot, this process will continue even after the wood
has been built into the house. At temperatures below +25 (77 F) wood
will not rot if it contains less than 20% humidity.
Another problem is that boards that are fastened while still
containing excess levels of moisture will dry after they have been
kept indoors for some months. This will cause the wood to contract,
and might cause unsightly cracks or deformations. Wood materials for
indoor use should only be used when it has been predried to the same
moisture levels that can be expected in their final environment.
On the contrary, wood that is too dry when it is installed might
absorb humidity from the air and start to expand, causing similar
How can correct humidity levels be maintained during the building process?
- Wood material should be ordered with a moisture level that is correct for
their intended use.
- Wood should not be taken out from its plastic wrapping before it is used, and
opened wrappers should be resealed after they have been opened.
- The unfinished construction should be protected from moisture by building it
in a dry time of the year. If the construction process must take place in the
rainy/snowy season, a waterproof tent should be erected over the building
- Predried wood boards for indoors use should not be brought to the construction
site before the building interior is waterproofed, insulated, heated and dried
to 40-50% air humidity. Note that fresh concrete will give off humidity for
some days - avoid opening predried wood in this environment.
- The roof should be constructed in a manner that prevents the outside wood
panels from direct rainfall.
- Boards on the outside of the building should be waterproofed (painted or
stained) as soon as possible after installation, or even before installation
if this is feasible.
I hope this answers your question. If not, please request an answer
clarification before you go on to rate it.
Clarification of Answer by
07 Dec 2003 04:28 PST
The wood framework of a new house will almost always contain some
excess moisture when the primary construction is finished - that is
when the roof and the outer walls have been finished. At this stage,
it is common to dry these materials by setting up some kind of air
heater (powered by electricity, kerosene or propane) inside the
construction to heat and dry the wood.
It would, of course, be possible to use wood that is rot resistant -
either naturally (such as sibirian larch) or by chemical treatment.
However, this will turn out to be quite costly. Also, some kinds of
the chemically treated wood contains toxic substances (such as
arsenic) which could be undesireable in a residential house.
Where I live, it has also become common to use wood boards that has
been waterproofed (by painting or staining) before they arrive at the
construction site. These boards are used to cover the outer walls, in
this way the walls are waterproofed immediately. This procedure can
also turn out to be less expensive than having the boards painted
If there is a significant risk of humid weather when the house is to
be built, it should be considered if a protective tent (as described
in the original answer) should be used. This will also provide a
better work environment for the people doing the construction work,
and might actually shorten the time needed to finish the house. I
have seen such tents being used, but I do not believe that they are
very common yet. I guess most house builders believe that the drying
process (as described above) will remove enough of the moisture.
There is probably no sharp limit for how long it is "safe" to leave
the wood in the rain before one should cover and dry it.