Basement renovation
Hi Martin:
We have had some issues in our basement – mold growing in the rafters on our unfinished side of our basement. (other half has drop ceiling and painted cement walls) We had professional come out and remove the growth from the half of the basement with the exposed beams/mold. The strange part is we dont’ see any water and every contractor comes in and says there is no signs of water (smell, moisture etc). Humitidy runs around 45% in the late summer when I started to track. We have 3 leaky windows on the unfinished side, and a back door with cement steps to the outside. We are also looking to renovate the “partially finished” side as a playroom. I need some guidance before I renovate to cover everything.
Considering the orginal mold insult, I am worried about renovating the
basement since we haven’t found the “source” of the moisture. 1) we plan on
replacing the windows. 2) we are considering either re-cementing our back steps
or putting in bilco doors/ prepoured steps, 3) insulating the walls. I guess the stack
effect isnt helping either (we have a strong draft with our chimney). The moisture must be pulled toward the steps in the basement – and moisture condensing on the rafters = growth
Is there anything else we should consider while finishing off 1/2 of the
basement? we have never had water – we have a poured foundation with no cracks. The previous owner stated they received water through the back steps during a hurricaine when the drain at the bottom of the steps became overwhelmed and water entered under the door. That may have been the reason for the growth if the water was not removed quickly.
I put in a dehumidifer as a precaution. But I don’t want to rip ou the basement in a few years if the mold returns.
Thank you
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
V Santa,
The first steps are to perform air sealing work and replace the windows. (This won't change the moisture situation, but it will save you energy.)
The next step is to check the grading around the exterior of the house, to be sure that your soil slopes away from your foundation. If your house is on a hill, you'll need to create a swale (drained away from your house) on the uphill side.
If your house has no gutters at the eaves, install them. The conductor pipes should carry the roof water away from the foundation.
The next step is to tape a piece of polyethylene to your concrete floor and concrete wall. Leave it there for 24 hours. If there are beads of moisture behind the poly, you still have a moisture problem.
(By the way, there are no rafters in your basement. You're probably talking about floor joists.)
You don't need water to get mold, only water vapor (humidity).
Follow all of Martin's recommendations and then heat the basement (I assume it's not conditioned now). Once you tighten it up and put heat to it, the relative humidity will drop to tolerable levels.
Running the dehumidifier in the meantime will help.
And install the Bilco bulkhead door. You may not have to change your existing concrete stairs as long as you can keep rain out of them.
When you had someone remove the mold, do you know what process was used?
The mold remover put down Shock wave? Then used a coating on the floor joists (thanks Martin)
Martin, I have gutters all running out about 6-8 feet from the foundation. I am not on a hill. The back steps could be a source of moisture and I will do the polyethylene test. Can I get some polyethylene at a Lowes or HD - is it a plastic bag material I am looking for?
The mold grew mostly on the joists running from the windows (old and leaking) toward the stairs to the 1st floor. the mixing of the air temps may have caused the moisture to condense - only thing I can think of. I will start the testing you suggested this weekend.
I will see if I can add a few vents in our ducts to warm the basement.
Thank you again