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Attic Rain

Updated: May 26, 2020

What is attic rain?

When humidity gets trapped or there is just too much inside the attic, it will build up as frost on the roof sheeting, as the temperature warms the frost will melt and drip down and starts to rain in your attic. If left unchecked, it can cause rot, mold and damages to the ceiling and exterior walls.

Why now? A house that is 100 years old may have never had attic rain in the past, but after upgrading windows and the furnace now it is starting to have problems. As we improve the efficiency of our homes it changes how all the components work together. Upgrading the windows and the installation of a HE furnace air seals the house and reduces air changes, this can increase humidity. If the humidity is allowed to escape into the attic, it can build up on the roof sheeting.

Attic rain
Water droplets inside your attic

Drops of water

When things start to warm in the attic, the frost starts to melt and will drip down into your insulation and eventually down to your ceiling or exterior walls.

Water stains

If you have access to your attic, you can check for water stains on your insulation, some types of insulation will look like a beach after a nice rain.

Look for frost

Small localized amount of frost can occur, but if you see the majority of the sheeting covered in frost you will have attic rain.

Bathroom exhaust fans

Bathroom exhaust fans that discharge into the attic is a huge source of humidity, make sure that they discharge to the exterior.

Bathroom fan discharging into your attic
Bathroom fan discharging into your attic


The proper type and amount of ventilation will help reduce air from being trapped in the attic, reducing the chance of frost building up.

Ceiling penetrations

Any penetrations in the ceiling like pot lights and attic hatches should be sealed to help reduce the chance of air loss into the attic.

What to do about it?

There are many things that can cause it and many options and ways to fix it so If you see signs or suspect you may have frost build up in your attic, you should get professional help to solve it, but here are some things you can check.

Make sure bathroom kitchen and dryers are vented to the exterior and the exhaust runs are hooked up, sealed and not kinked. Turn on your fans and see if you can find where they discharge on the exterior and confirm for air movement.

Attic condensation
Attic condensation

Seal off any spots for air to leak into the attic, this includes pot lights, attic hatches, exhaust fans, around interior wall electrical plugs and switches.

Reducing the humidity in the home. If your home has an HRV, make sure it is being used the filters are clean, along with the exterior intakes and exhausts. I will be talking more about HRV's in the future so keep an eye out for it.

As you can see there are many things that can affect a house and the chance of attic rain, to find out more or to book an inspection contact us.

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