How should I vent the attic above one room?


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Old 08-12-21, 08:57 AM
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Question How should I vent the attic above one room?

We recently had our whole house insulated with closed cell spray foam but they wanted 1k to do one room so we passed. Well with the heat we are now experiencing in Portland, I decided to insulate it myself so I put 2" rigid insulation in-between the rafters and R-30 bats on the ceiling and it has helped immensely!
Now I would like to vent that attic to let the hot air out in the evening. I have a metal roof and would rather not go through that if I don't have to. I read about whirlybirds but how do they do if there's little wind? So I was thinking of going out the gable wall with a fan that has a thermostat but I don't want some big 12x12 thing either on the wall either. I was thinking maybe a large bathroom fan might do the job hooking that up to a thermostat.
Anyone have any other ideas? Oh and thanks for your time looking at this!

Gable wall

Attic 11'x11'
. The attic ceiling space is 11'x11'. Attached are pics of the attic and the exterior wall.
Thanks in advance for any advice!
 
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Old 08-12-21, 10:14 AM
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So this is just an attic, not a living space?

It appears your attic floor/room ceiling is insulated so adding insulation to the underside of the roof was not needed, all that is going to do now is hold heat generated in there during the day longer!

If your going to exhaust air then you also need to consider a way to let air in!

A powered, thermostatic exhaust fan really is an option unless you go with some form of passive ridge/eve venting!
 
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Old 08-12-21, 11:48 AM
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Thanks a bunch for your response!
So I went overkill, lol, typical. Yes, it is not a living space. So what you're saying is I need airflow. Not sure how I should handle but you're saying an thermostatic exhaust fan. I have a thermostat (from a grow room) that I can use so do you think a bathroom type ceiling fan vented out will help get the hot air out. And what about winter, will it be the opposite affect?
 
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Old 08-12-21, 04:22 PM
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do you think a bathroom type ceiling fan vented out will help get the hot air out
Long term no, just google "thermostatic attic fans". They make them that go through walls, through roofs, that is what they are designed for.

But again, it you exhaust air you need to have a way for fresh air to enter. Out at the peak, in under the eves is most efficient!
 
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Old 08-13-21, 03:02 PM
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Thanks!
There's one that's 10" so I guess not too bad. I'll look into different types of vent options for soffits. Is there a rule of how many I need for such a small room? For 4" round ones, every 3rd or 4th rafter cavity?
 
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Old 08-13-21, 11:08 PM
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For static venation its 1 sq ft f opening per 100 sq ft of floor space.

For power ventilation I would think less but Id start with the manufacture for guidelines!
 
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Old 08-14-21, 05:49 AM
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If you don't have or don't want a roof ridge vent then the next best thing is a vent in the gable on each end, as high up as possible.Put a large fan in one of them.

The attic remains open to the outside year 'round.

With the attic floor insulation resting on top of the joists, you cannot avoid stepping all over the insulaiton to do work up there. Or you can build a catwalk of 2x6s upright on top of the joists and 1x10 (more or less) planks on top of that.
 
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Old 08-14-21, 08:37 AM
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There is only one gable end in that room. They added the bedroom probably 40 years ago and just stuck on the side of the house. There wasn't even an access door into the attic until I cut one from the adjoining attic room (the siding is still on the house side of the room up there) that has vaulted ceiling and it is spray foamed. I have 1/4" plywood that serves that purpose of moving around up there. It's kind of a unique situation and why I'm here talking to you guys that know your stuff! Oh, the metal roof is brand new and the roofing contractor is a jerk along with the gutter guys that put the gutters up level so the flow sucks! They won't answer my calls..... I would rather not mess with the roof.
Thanks!
 

Last edited by drumz; 08-14-21 at 08:40 AM. Reason: more info about roof ridge
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Old 08-14-21, 08:48 AM
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contractor is a jerk along with the gutter guys that put the gutters up level so the flow sucks!
You might owe an apology for that, slope for gutters is not needed, personally I hate the look of a long run of gutter that has slop it looks terrible, I always install level. First it ensures that the gutter back is tucked under the drip edge and second, the gutter doesn't need slop, it will drain as it fills and any small amount of water remaining will simply evaporate!

As far as the exhaust, just get the inlet and outlet as far apart as possible so there is flow across the attic!
 
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Old 08-14-21, 09:13 AM
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I'd consider putting a smaller copy of the window in the peak, probably use a single shutter to clear the decorative eaves.

Post Script
Originally Posted by Marq1
It appears your attic floor/room ceiling is insulated so adding insulation to the underside of the roof was not needed, all that is going to do now is hold heat generated in there during the day longer!
I wouldn't be so sure about that with a metal roof, BUT there should be vent baffles against the underside of the roof to prevent condensation and rotting.
In my situation (uninsulated roof) I actually found that a layer of Styrofoam vent baffles DID help by reducing the amount of radiated heat coming from the underside of the roof.

EDIT TO THE EDIT
I've got a somewhat similar situation, but with a 1½ story saltbox attic instead of a ½ story peak attic.
What I've done is lay unused vent baffles across the collar-ties to create a triangular area to trap rising hot air, AND block radiant heat from the roof, which means the hot air passively exhausts through the gable wall via an unused chimney (which creates
Meanwhile, I've got a fan on a thermostat providing active ventilation to the main area which I use for a library & bookshelves, file storage, and backup office.

What I've found is that foam baffles pull hot air up along the undersurface of the roof and then exhaust it at the peak. So, at 2pm in summer the air above the foam barrier at the collar ties is usually over 120°F, but the air below the collar ties stays around outside temperature, say 85°F.

If I were you, I'd consider something similar: make sure your between-the-rafters insulation is NOT up against the underside of the roof, but has a gap for air flow. I'd prop up some extra insulation above the collar ties to make a leaky "duct" (rough outline in blue), and see about adding a vent at the left top of the gable wall (about the size of the red square, but through that exterior gable wall).

Curious what others here think?


 

Last edited by Hal_S; 08-14-21 at 10:10 AM.
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Old 08-14-21, 09:45 AM
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Originally Posted by AllanJ
If you don't have or don't want a roof ridge vent then the next best thing is a vent in the gable on each end, as high up as possible.Put a large fan in one of them.
My sister's house was suffering from this issue where the exterior paint was melting/chipping off the wall at the gable areas. This is exactly what I installed; vents to alleviate the heat. I did put in a gable fan and it helps.

The only problem with open attics, it invites terminates.
 
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Old 08-14-21, 09:59 AM
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More pics for a better idea of room layout


A better shot of bedroom and relationship to house.

Backside of the bedroom. Ridge cap is solid so would have to be removed, vents cut and then a new vented roof cap. I do not want to go through that much work...

This is from the attic room with the access door on the left that I cut to get access to the bedroom attic I'm wanting to cool down.
 
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Old 08-14-21, 10:35 PM
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The only problem with open attics, it invites terminates.
Termites??

Going to have to explain that one!
 
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Old 08-15-21, 04:51 AM
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Hahaha, type error. Thanks for catching it.

Termites.

We live in an area where winter gets damp and my neighbors were sharing that rodents, bugs and termites enter the house through the gable vents.
 
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Old 08-15-21, 06:59 AM
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Question- do you have ANY ventilation as part of the new roof installation?
If the lower roof doesn't have any ridge or gable vents, does it at least have soffit vents?
Same question for the roof on the main building, is there any ventilation?

If there is ventilation in the main roof, it seems like there may be a simpler way to vent the addition-

I would consider adding a cool air inlet vent at the bottom of the access hatch BLUE RECTANGLE and then cut a hot air outlet connecting the airspace of the addition to the airspace behind the knee-wall of the bedroom. where the rooflines join RED TRIANGLE so that you'd at least have some connection to main roof venting system.
If the main roof doesn't have a venting system, I'd check whether the plans that the contractor submitted to the municipality to get a building permit included some sort of attic venting...



 
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Old 08-15-21, 08:22 AM
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There are no roof vents anywhere on the new roof. We did the remodel with only an electrical permit. Behind the knee wall on both sides is open but no venting there either. There are soffits around the entire house but no venting. It's been 3 years since the remodel and we have no issues with moisture or anything and the house is way more comfortable than the original built in 1942 which is in a rural part of the city, few neighbors but lots of bugs and critters so keeping them out is a priority. Contractor was stealing from us so we fired him two months in and the lead who is licensed was sick of him screwing ppl too so he quit and stayed to help finish. We did everything except: heat vents, sheetrock, some plumbing, cement work, spray foam, roof and gutters. We only added 300 sf to the footprint but had to tear out half the house from a previous remodel because there was no footing on the foundation which quite possibly could be the same under the bedroom since it seems they were both done fairly close together - no permits on that job either so we continued the tradition d;-)>
 
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Old 08-15-21, 08:48 AM
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Originally Posted by drumz
There are no roof vents anywhere on the new roof.
Eh, then I'd consider hiding at least some small vents in the peaks.

Carefully pop off the wood shingles, add a gable vent with steel critter screening, and then re-place the wood shingles using 1 inch spacers- that gives you the look of a shingled wall, BUT gives sufficient space for some passive airflow.

Most older homes are "leaky" and you don't need to worry too much about passive ventilation.
If not, leave a window on the cool shady side of the house open a bit.


 
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Old 08-15-21, 09:20 AM
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So are you saying forego the exhaust fan and just vent it like you proposed?
 
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Old 08-15-21, 11:13 AM
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Originally Posted by drumz
So are you saying forego the exhaust fan and just vent it like you proposed?
Not exactly, but passive venting of hot air is better than no venting.
If you have some spare large diameter HVAC vent tubing, you can also get "creative" with your exhaust fan setup.




Vertical siphon for peak

Venturi exit for peak siphon
 
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Old 08-15-21, 11:43 AM
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Thanks for all you information, very helpful!
Here's my plan, cut a vent in from back side of the knee-wall and then put the 10" thermostatic attic fan in the gable wall. I checked with the manufacturer about the size sharing my dimensions and they said 10" would be enough.
 
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Old 08-16-21, 06:38 PM
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H uses 1600cfm roof fan at upper section of split level with 24” window fan blowing in at other end of attic. One ordinary thermostat activates both, set just above local night time temperature, say 90F. For air intake, which should be twice fan area, have screened louvers under eves around house.

Would not use built in-switch on most fans. They often does not activate until 100F to 120F+.

Here is a link to wide collection of ventilation fans:

https://www.amazon.com/s?k=roof+fans...s_ts-doa-p_4_8
 
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