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New steel roof, has condensation on it...

Hi everybody!

We purchased a house this summer, and three days later after a big rain, the roof leaked. Needless to say, we wound up replacing the entire roof, as there was no way to repair it.

We ordered up new trusses, and steel for the roof. We installed the trusses with perlings and then laid the steel over top. I couldn't get a straight answer out of anyone regarding tar paper.

I have vented soffit on three sides and a ridge vent the entire width, which is 12' I have only insulated with R-30, which is 10", so far, was going to do a better job and add some more insulation before sheet-rocking.

My problem is, I pulled the edge of my plastic and one piece of insulation down so I could run my plumbing stack through the roof, and I have condensation on the underside.


Re: New steel roof, has condensation on it...

Did you do the work yourself?

Without knowing all the facts, I will guess that you attached your insulation to the metal roof from the inside without spacers, which is the wrong way.

More info needed.

Re: New steel roof, has condensation on it...

There should be a continuous air gap from the eave to the ridge between the roofing and the insulation -- the insulation should not be in contact with the roofing. This will allow air to flow and remove moisture.

Normally, rather than tar paper, a heavy plastic sheeting product called 'scrim' is used. The scrim protects the metal roofing from any moisture that does condense on the underside. Tar paper isn't recommended because it's not fully supported by full plywood sheathing; over time it will become brittle and fail when it's only supported by the purlins.

Since it's rather difficult to install the scrim after the fact, you can remove the existing insulation and have expanding closed-cell spray foam applied on the underside of the roofing to 1" thickness. This will provide the necessary protection to the roofing. Then reinstall your insulation. An advantage is that you won't need to provide any air space or vents at the eaves and ridge, though you will want to provide a bathroom-style exhaust fan on a timer (or a heat recovery air exchanger on your furnace) to provide periodic air exchange to get rid of the moisture that will inevitably build up inside the house.

Of course, this is all speculation based solely on your post. There may be more relevant information that renders my recommendations invalid.

Re: New steel roof, has condensation on it...

The insulation is not touching the steel. The insulation is at the bottom of the truss. I installed chutes at the end of each cavity right by the soffit.

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