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Carling 06-05-2013 10:35 AM

Wooden Soffit/Aluminum Soffits + Attic ventilation
 
I am currently in the process of putting up new fascia/soffits/eaves on my older home. I currently have wood fascia board and old rotted out eaves.

I've purchased some of the peak products that are sold in home depot and I am trying to understand what is the adquate ventilation that's requried from the soffit.

Current aluminum soffits have multiple holes in them for air inlet, I've seen roofers install these right over wooded soffits. This to me makes no sense and I am trying to understand if that's correct. The attic needs air inlet and outlet, the basic formula is 1 square foot of air intake/outlet for every 300 square feet of roof. The way I understand this is that for every 600 sq. ft. of roof you need 1 sq. ft. of air inlet (at soffit) and 1 sq.ft. of air outlet vent on actual roof. That's 2 sq. ft in total for 600 sq. ft so 1:300

Having said that my house currently meets this formula of 1 : 300, however my air inlets at the soffits are cut outs in the wooden soffits and seem small and need to be opened bigger.

I've called peak products and asked their customer service what the proper way to do this is and how do their soffits affect air ventilation in the attic if they are put over wooden soffits with a few cutouts actings as air inlet vents. He said you can either put them under the existing wood soffits as is or rip out the old wooden ones and just put their aluminum soffits throughtout (this is how it's done on new construction).

To me it makes no sense that both ways are identical when one obviously allows for more air to enter the attic and the other one is a lot less. Obviously too much air or too little air entering the attic will have different negative effects so I am trying to figure out what approach to take to continue keeping the attic at the 1:300 rule.

Another question is, the new aluminum soffit vents and their small holes: is it safe to assume that those little holes are designed to function by the 1:300 rule? Meaning there are many small holes, obviously there isn't a single opening that's 1 sq. ft. but if the soffit was placed along the edge of a 300 sq. ft. roof area, do all those little holes add up to 1 sq ft of air intake?

gregzoll 06-05-2013 11:22 AM

Went over this in 2012 http://www.diychatroom.com/f9/attic-...s-pics-150894/

Carling 06-05-2013 12:29 PM

Quote:

Originally Posted by gregzoll (Post 1195666)


Doesn't answer my question...putting aluminum soffits over wood or ripping all wooden soffits and replacing with aluminum.

Also, does the aluminum soffit work with the 1:300 rule based on the hole sizes.

gregzoll 06-05-2013 12:46 PM

It is really up to you what you wish to do. Wood needs maintenance, where as Aluminum does not. Now if you are in an area that gets a lot of Salt water, or salt in the air like around Salt Lake City, UT, then you want to use wood.

Carling 06-05-2013 01:53 PM

Quote:

Originally Posted by gregzoll (Post 1195702)
It is really up to you what you wish to do. Wood needs maintenance, where as Aluminum does not. Now if you are in an area that gets a lot of Salt water, or salt in the air like around Salt Lake City, UT, then you want to use wood.


I am in Toronto.

My main concern is how much air inlet will there be if I run aluminum soffit with no wood under, would that be too much? And if I run aluminum soffit with wood under (the stuff I currently have) will that be enough air inlet?

Carling 06-05-2013 02:06 PM

Also, here is why I am confused based on the responses from the other thread:

Some of the suggestions, no concrete answer:

Quote:

Those appear to be 16" X 6" (?) with 37sq.in. NFVA, at 9NFVA per foot for soffits (1/300) they should be every 4' apart;
Quote:

For the 1/300 rule - 1371/300 *144 = 658 / 2 = 329 sqin NFA for intake. You have 5 x 37 (based on GBR's info) for a total of 185 - If you want to add more add at least 4 equally spaced where air would be drawn out of exhaust vents. It won't hurt to add more than four to get the air balanced correctly.
Quote:

I'll stick my neck out and say it, "continuous soffit venting is for ice dam problems only".:laughing: Soffit venting is not the perfect solution, but a compromise between not being able to best insulate along the eave and trying to keep the roof deck cold.
Unless you confirmed having ice dam, and you've confirmed no mold, it is possible you are just letting in more cold air. If no ice dam, dead air space is better in winter. Roof fan for some cooling in summer. Both are easier retrofits.
Quote:

I only put in fully vented soffits and I put a chute in every rafter bay, even when retrofitting. I've never heard about any negative effects because of this.
Quote:

When retrofitting an attic which has a soffit vent here and there, I've never learned how many you need, other than the 1/300 rule. I guess what I'm trying to say is, if you want all those chutes to flow air, it won't work if you have only a soffit vent here and there. The chutes closest to the soffit vents will hog all the air going up to the exhaust vents and this will result in hot spots.

Carling 06-05-2013 02:07 PM

Ultimately I'd like to know if the aluminum soffit venting holes are designed to work with the 1/300 rule?!?!

gregzoll 06-05-2013 02:10 PM

All of the info is there in the other thread, and GBR is an expert to this stuff, and quote two is what you needed to know.

As for support, if there are extensions on the rafters to support the facia, that will be there to help support the channel, that supports the soffit material. Personally I would go with Aluminum material full perf, and then use baffles in each bay, so that you get enough airflow in through the attic.

If you put a remote sensor up there now as is, what are the current temps and relative humidity readings that you are seeing?

Carling 06-05-2013 02:18 PM

Quote:

Originally Posted by gregzoll (Post 1195731)
All of the info is there in the other thread, and GBR is an expert to this stuff, and quote two is what you needed to know.

As for support, if there are extensions on the rafters to support the facia, that will be there to help support the channel, that supports the soffit material. Personally I would go with Aluminum material full perf, and then use baffles in each bay, so that you get enough airflow in through the attic.

If you put a remote sensor up there now as is, what are the current temps and relative humidity readings that you are seeing?

That's a good point, I should measure the difference in humidity in attic and house, as well as temps. That might give a bitter idea, I will do this shortly. It's pretty cool today so I don't think it will be of much value.

gregzoll 06-05-2013 02:38 PM

It is 79 around 55% rh outside at my place, 94 in the attic, 19% rh up there. My attic exhaust fan does not kick in until around 95-96 degrees, and we have six vents along the peak to help with passive exhaust, along with two vents on the ends on the gables.

Before we got the power vent, it would get up to 130-135 up there, just with the passive venting.

Carling 06-05-2013 03:22 PM

Quote:

Originally Posted by gregzoll (Post 1195741)
It is 79 around 55% rh outside at my place, 94 in the attic, 19% rh up there. My attic exhaust fan does not kick in until around 95-96 degrees, and we have six vents along the peak to help with passive exhaust, along with two vents on the ends on the gables.

Before we got the power vent, it would get up to 130-135 up there, just with the passive venting.


I have a feeling a power vent like that would be really good for me.

Not sure where humidity was in the attic, but it was hot, inside the house on hot days it gets up to 75% sometimes :eek: at 77F. I'd have to turn the A/C on for 20-30 mins and it would go down to 60%. This is part of the reason I think something is wrong with my venting.

House is bungalow too, so my measurement on my main floor is technically my top floor measurement.

gregzoll 06-05-2013 04:35 PM

You need something like the Radioshack Weather Forecaster with remote sensors, which I use, to keep tabs on my attic, basement, and living room area temps/humidity levels.

As for set point on the thermostat, it helps to have the house leaks around windows, doors, attic hatch, outlets on outside walls sealed, any openings into the attic from flu ducts, wiring, sealed, baffles along the soffit line, to help air movement.

As for the hvac, it also helps if the unit is in good shape, and sized properly to allow it to run at its best.

We have a older 70+ year old home, but during cooling & heating, I close the storm windows to help with more efficiency, also we have UV film on all windows to help cut down on heat gain, along with using darkening drapes on all windows, but the two in our Kitchen. That alone has helped cut down on gain on the South side.

We did go half a ton higher to a 2 ton unit for our a/c, which is only Single stage, but our Lennox Signature Series furnace is a 2-stage unit, which helps especially during cooling season, along with I use a 3m-50 thermostat with a Our Home Spaces radio module, to allow remote monitoring and control of the system while in the home, or away.

When I first got the thermostat, there is actually a software made for the RTCO (Radio Thermostat Co) radio api, that I could sit there and track run times, how fast the thermostat would change from temp when the ac or heat stopped, and when it would kick in.

On a 94 degree day, with 80% humidity, we can see at most our system may run two maybe three hours max, but that is because I have trees to help shade the roof line, the power vent to help keep the attic temps down to at least no more higher than 110.

It is more of a lot of play and brain work to figure out a medium when dealing with homes, and especially when the original builder back in the day did not know about what the hvac systems of today would be like, or how to make the structure efficient.

Around here, the most anyone really keeps their thermostats is, is at most 74, but most are around 72 on average during Summer, Winter around 68-69. At night, I have found talking to people, that they stay anywhere between 62-65, 60 while away during Winter, 72-74 while away during Summer, 76 if no pets in the home.

I just ended up keeping ours at 70 at night, 72 day for Summer, 65 at night, 69 day during Winter. If it gets bad with the pollen outside, and I have to keep the house closed up, then I may adjust the thermostat to at least get the system to cycle once or twice an hour, because the attic again still even if it say 58 outside, with 80% rh, I have seen it get up around 70 with around 21-23% rh up there.

Carling 06-10-2013 01:24 PM

Quote:

Originally Posted by gregzoll (Post 1195800)
You need something like the Radioshack Weather Forecaster with remote sensors, which I use, to keep tabs on my attic, basement, and living room area temps/humidity levels.

As for set point on the thermostat, it helps to have the house leaks around windows, doors, attic hatch, outlets on outside walls sealed, any openings into the attic from flu ducts, wiring, sealed, baffles along the soffit line, to help air movement.

As for the hvac, it also helps if the unit is in good shape, and sized properly to allow it to run at its best.

We have a older 70+ year old home, but during cooling & heating, I close the storm windows to help with more efficiency, also we have UV film on all windows to help cut down on heat gain, along with using darkening drapes on all windows, but the two in our Kitchen. That alone has helped cut down on gain on the South side.

We did go half a ton higher to a 2 ton unit for our a/c, which is only Single stage, but our Lennox Signature Series furnace is a 2-stage unit, which helps especially during cooling season, along with I use a 3m-50 thermostat with a Our Home Spaces radio module, to allow remote monitoring and control of the system while in the home, or away.

When I first got the thermostat, there is actually a software made for the RTCO (Radio Thermostat Co) radio api, that I could sit there and track run times, how fast the thermostat would change from temp when the ac or heat stopped, and when it would kick in.

On a 94 degree day, with 80% humidity, we can see at most our system may run two maybe three hours max, but that is because I have trees to help shade the roof line, the power vent to help keep the attic temps down to at least no more higher than 110.

It is more of a lot of play and brain work to figure out a medium when dealing with homes, and especially when the original builder back in the day did not know about what the hvac systems of today would be like, or how to make the structure efficient.

Around here, the most anyone really keeps their thermostats is, is at most 74, but most are around 72 on average during Summer, Winter around 68-69. At night, I have found talking to people, that they stay anywhere between 62-65, 60 while away during Winter, 72-74 while away during Summer, 76 if no pets in the home.

I just ended up keeping ours at 70 at night, 72 day for Summer, 65 at night, 69 day during Winter. If it gets bad with the pollen outside, and I have to keep the house closed up, then I may adjust the thermostat to at least get the system to cycle once or twice an hour, because the attic again still even if it say 58 outside, with 80% rh, I have seen it get up around 70 with around 21-23% rh up there.


Great info and thanks for the post.

Carling 06-10-2013 01:25 PM

As promised we had a decent Sunday here, I didn't run a/c or heat, this is what I measured in the house mid day:

http://i44.tinypic.com/a2q8t5.jpg


This is what was in the attic at the same time:

http://i44.tinypic.com/2rpcytx.jpg

Carling 06-10-2013 01:27 PM

Also, I called peak products, which are the main suppliers of aluminum soffit vents to Home depot and I finally got my answer.

The "net free area" of their vented soffits is 4.6" of vent for every square foot. This is basically what I was looking for in order to find out if venting all around will work with the 1/300th rule or if it would be too much. Just an FYI for everyone else looking for this info.


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