Thread: Mold after renovation

Hi there,

My client has an old 1950 duplex in Montreal. The exterior siding used to be aggregate and they've never had any problem.

He recently called a company to install Vinyl siding all around the house and he also changed his old windows for a new PVC with thermos model.

So the contractor simply took off the exterior aggregate siding, he installed +/- 2 inch polystyren insulation panel, then he put the vinyl siding.

2 Weeks ago, the temperature dropped and we started to have cold weather, thats when they realized they have mold on the bottom of their exterior wall (from inside).

When I opened the wall, I noticed a funny structure but most importantly that there was no insulation. Only two sheets of plaster before the structure, then you could see the original solid wood siding.

I didn't notice any mold or humidity inside the wall, but only on the surface of the plaster.

Here are my questions:

1 - Why is there mold only on the surface and not inside the wall (since I thought the cause of the problem is the lack of insulation).

2 - Why is the mold present only on this particular wall and not the others since all the exterior siding has been changed.

3 - How could an exterior wall hold and support the upper floor weight without 2 x 6 structure like I normally see.

Sorry for my bad english, I'm french canadian : P

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The mould is growing on the inner surface only. That is not unusual in a house that is poorly heated. It is likely due to a cold spot, poor air circulation, and moisture in the interior air condensing on the cold surface of the drywall.

Your client should look at blowing insulation into those wall cavities. A contractor can remove some vinyl, drill holes and blow cellulose in. But since you are pulling drywall already, it can be done from the inside.

Rough-cut 2X4's are typical for the age of the house. Those studs do look like they are only about 3". That is questionable, for sure.

Part of the problem in photo two - the exterior replacement siding and insulative panels are poorly installed.

I suspect that part of the problem has to do with how the house now breaths.

Originally Posted by Eric Barker

I suspect that part of the problem has to do with how the house now breaths.

... or does not breathe ...

... at least not like it did in its original state when the house worked with itself and not against itself.

I agree with all the above.


CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Applications Consulting Technologies, Inc. - Home

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

Definitely the air in the home condensing on the wall. That is the reason there is no mold on the inside.

Originally Posted by Jerry Peck

... or does not breathe ...

... at least not like it did in its original state when the house worked with itself and not against itself.

What recommendations would you make?

Originally Posted by Jerry Peck

... or does not breathe ...

... at least not like it did in its original state when the house worked with itself and not against itself.

Originally Posted by Lon Henderson

What recommendations would you make?

To contact someone expert in building science to make recommendations on what needs to be done to correct the condition(s) found.

Not that I did not say for someone to "evaluate" the building - they *HAVE* to do that in order to make their recommendations on what needs to be done, *I* do not need to tell them to "evaluate" the building.

When I opened the wall, I noticed a funny structure but most importantly that there was no insulation. Only two sheets of plaster before the structure, then you could see the original solid wood siding.

The interior wall due to lack of insulation is now reaching its dew point thus creating favourable conditions for mould growth.

Also

Guide to Insulating Sheathing
Guide to Insulating Sheathing — Building Science Information

Incidentally how is this house heated?