Roof / Attic Ventilation Inspection

Post 126 of 157

This is a very extensive topic, so please use reference links to my other posts, especially if everything is new for you and you really want to do most of the inspector’s work.

The house roof / attic needs to be ventilated for its own and home owner’s benefit – non or poor ventilation might create the perfect mold growing environment … so let’s take a look at it.

The general idea (minimum requirement) for a proper roof / attic ventilation is 1sq foot of ventilation for every 300 sq. feet of attic space divided 50 / 50 between the inlets and outlets – assuming that everything else is perfect…

If your pitched roof has an overhang (it doesn’t end even with the house exterior wall), there should be venting ports installed underneath / along the soffit – they come in different shapes and styles – more is always better than less – you can see that on pictures in Attic Mold post. These vents are called “inlets”, and if you don’t have any installed, there’s a significant chance, that your attic has been already mold contaminated (exceptions happen). There are new types of vents offered for the roofs without overhang, which should solve ventilation problems in this design – vented drip edge, which installs along the roof edges, and hip vents.

There should be vents located on the top section of the roof playing the “outlets” role, and again – more is better than less, because with less than necessary, moist and warm air might get trapped in the attic during the cold season and condensate on decking surfaces creating ideal mold growing environment. There are many different types of vents (check Attic Ventilation post), but you just need to make sure that they are properly installed on your roof and that they are open / clean (if you can’t see any – you might have a “ridge vent” installed which is also a good choice). Larger size vents on the roof surface are usually turbine (wind) and electrcial motor powered vent – they should be functional.

If your house has vaulted / cathedral ceilings (complete or partial) – they, too, have to be ventilated! If you have no attic, but have cathedral ceilings through the house, you should have a ridge vent installed and continuous soffit vent or venting in each rafter space (approximately every 16″ – doesn’t look nice, and ridge vent is much better for such application)

You might also have gable vents installed (depending on the roof type), which also serve their purpose well.

Assuming that you have visible vents on the roof, in the gable, along the soffits and accessible attic – they should be checked from within the attic –

don’t do it if you’re not 200% sure that you can handle it. During the summer, in a poorly vented attic, temperature might be around 150F. Plus you have to watch where you are stepping – get a professional for this venture.

Vents are usually protected from birds and rodents with screens, but they love to build nests inside them which have to be removed to provide proper air flow (Attic Ventilation post). Rodents sometimes damage screens and manage to penetrate the attic, so it’s a good idea to have the attic checked on a regular basis.

Electrical motor powered vents should have a thermostat, all connections must be secured and inside the conduit – no exposed wiring, loose connectors, and fan blades should be moving freely, and respond to the thermostat setting. Don’t touch the blades with your hand – they are razor sharp, and the motor might start automatically! If the blades are hard to turn / stiff, or are not turning at all – it is usually a burned out motor – use a wooden stick to move them!

Look at the surface of the roof structure and decking (plywood or wooden boards) for unusual residue, discoloration, stains, etc. If there’s a ventilation problem, the mold will usually start along the lower portions of the attic (where the roof meets the attic floor) and above the bedrooms and bathrooms.

Bathroom exhaust vents have to discharge to the exterior! They are one of the main heat and moisture sources – make sure that there’s a pipe connected to the exhaust fan discharge port which extends through the roof. It might be also secured near the roof vent, but don’t block it.

Good luck!

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This article was written by Dariusz Rudnicki

I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local

2 comments:

gary at Reply


we have an older cottage with no ceiling.just the old open rafters and no insulation in the roof area, the cottage gets real warm in the summer and we try using ceiling fans running in the reverse summer direction but they just drive the warm trapped air down. we are redoing the shingles and would like an opinion as to wheather adding some kind of powered attic vent system that could be controlled might help and then we could run the window AC unit with th colder air actually making a differance as the warm air at the ceiling can be removed. I have considered that simply adding a few roof vents would help a certain amount but we also use a fire place and small heaters when the weather is cool and would not want all the warm air going out the roof. Would love to hear an opinion. we do not expect perfect living conditions but jus to hear might work best.

Dariusz Rudnicki at Reply


Hi Gary,
Without the ceiling / roof insulation it’s going to be difficult to condition your cottage. AC is efficient only while recirculating air within some sealed area. Therefore, if you decide to add any roof vents, you’d have to install some type of mechanical dampers so you can close them whenever the AC kicks in. Otherwise you’ll be wasting lots of energy because all that cooled air will be gone through the roof.
Also make sure that the AC unit is large enough (BTU’s) to cool down the entire space (including your open attic). Combined with the ceiling fan it should condition the entire space quickly but because of the missing insulation, it’s not going to be efficient.
Roof vent dampers would also help while heating this area / prevent loosing heat. I’m not sure if your fireplace has an exterior combustion air port or it’s using air from within the house. If it is interior air, those future roof vents (if left open while using the fireplace) might cause an excessive draft and result in faster burning of the firewood. Also, if installed in a close proximity to the fireplace chimney, you might get some smoke back to the house.
So again, a damper equipped vent would help but you may need to improvise since I don’t think they make attic / roof vents with dampers. If you have a gable type roof you can install a gable vent with automatic shutters and control its operation with a switch or a thermostat. Gable would simplify this whole process.

Thanks and let me know if you have any other questions.

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