[nemo77]

Hi. I really need help figuring out this attic ventilation. I am getting mixed opinions from roofing guys and insulation.

I live in Northern VA. We have 2 18x24 gable vents, one on each side of the house. We also have an attic fan, controlled by temperature and humidity.

Is this enough for our ventilation?

Some people have said we have adequate ventilation.

If we don't have enough, one company has offered to cut in soffits vents for $800. We will be getting anew roof within the next 2 years. Is it worth that amount or is it better to go with something like a smart vent when the new roof is installed.

Thanks in advance for all the help/advice!!

 

[Windows on Wash]

PAV (powered attic ventilators) are usually a bad idea. Most run at negative pressures that suck conditioned air out of the living space below.

The best ventilation, assuming it is done properly, is balanced intake and exhaust that runs the full width of the roof and is adequate in terms of net free area (NFA).

 

[nemo77]

PAV (powered attic ventilators) are usually a bad idea. Most run at negative pressures that suck conditioned air out of the living space below.

The best ventilation, assuming it is done properly, is balanced intake and exhaust that runs the full width of the roof and is adequate in terms of net free area (NFA).

Thank you for the info. So, in your opinion i should get rid of the attic fan when i get the new roof and add soffit vents?

In my current system, are the gable vents considered the intake and the attic fan the exhaust?

Also, I forgot to mention that my sqft area in the attic is ~730 sqft.

Thanks again!

 

[Windows on Wash]

If it were me, I would be sure to add some soffits and go passive.

 

[Bud9051]

Assuming you get some cold weather in VA then you need to have ventilation during the winter as well as during the summer. In winter you are removing moisture that leaks into the attic where it can condense on the bottom of the roof as well as excess heat which can cause ice dams. The temperature controlled fan will not be operating in the cold weather.

Not sure what they are proposing for their $800 soffit vent install or what you have for soffits. The NFA (Net Free Area) you would want to add for the soffit vents would be around 2.5 ft². You would also want the same amount for high vents NFA with gable vents and a ridge vent. More on that if you would like.

Give us some details on what they were proposing for those soffit vents and what your soffits are made of.

Bud

 

[nemo77]

Assuming you get some cold weather in VA then you need to have ventilation during the winter as well as during the summer. In winter you are removing moisture that leaks into the attic where it can condense on the bottom of the roof as well as excess heat which can cause ice dams. The temperature controlled fan will not be operating in the cold weather.

Not sure what they are proposing for their $800 soffit vent install or what you have for soffits. The NFA (Net Free Area) you would want to add for the soffit vents would be around 2.5 ft². You would also want the same amount for high vents NFA with gable vents and a ridge vent. More on that if you would like.

Give us some details on what they were proposing for those soffit vents and what your soffits are made of.

Bud

Hi bud. Right now we have only an attic fan in the middle near the roof peak. It is controlled by a temperature and humidistat(for winters). It does get cold in the winters her in VA but usually not below freezing.

We also have 2 gable vents, 18x24. We have no soffit vents or ridge vent. Currently the covers on the soffits are there, but the wood in the soffits were never cut. So from the outside it appears we have soffit vents, but we do not have any air going through it.

The contractor is proposing to take off the soffit covers, cut the wood, and reuse the old aluminum soffit covers.


Yes, I would like more info on high vents NFA with gable vents and a ridge vent.

Thanks!

 

[Bud9051]

Two 18 x 24 gable vents at 50% NFA gives you about 3 ft² of vent area, which is good.
The metal covering your soffits can be a pain to remove and since the metal needs to be cut as well it might be possible to cut through both at the same time. An option where I would need to see to consider. Not sure if the new vents can be sealed to the soffits that way. Back up here for a second. Again I'm not sure what you have, but if those metal soffits can be replaced with vented vinyl soffit material then the job might be a lot easier. Some pictures might help.

However, what you have seems to be working and your moisture issues are not as bad as what we face here in the north country. If you currently are experiencing no mold or mildew issues in the attic then the soffit vents may be able to wait, especially at $800. When you replace the roof and add a ridge vent, then you can consider retiring the powered exhaust and going with natural ventilation. In any case the air sealing of the attic floor (ceiling below) should be done and your insulation should be at least code minimum.

Almost forgot. Attic floor area divided by 150 gives you your total NFA. With just ridge and gable vents there is not a lot of height difference and it is the height that helps to create the air flow. Gables will work with a ridge but may need a breeze to help. Unknown how well, but soffit vents can be added at any time.

Bud

 

[nemo77]

Two 18 x 24 gable vents at 50% NFA gives you about 3 ft² of vent area, which is good.
The metal covering your soffits can be a pain to remove and since the metal needs to be cut as well it might be possible to cut through both at the same time. An option where I would need to see to consider. Not sure if the new vents can be sealed to the soffits that way. Back up here for a second. Again I'm not sure what you have, but if those metal soffits can be replaced with vented vinyl soffit material then the job might be a lot easier. Some pictures might help.

However, what you have seems to be working and your moisture issues are not as bad as what we face here in the north country. If you currently are experiencing no mold or mildew issues in the attic then the soffit vents may be able to wait, especially at $800. When you replace the roof and add a ridge vent, then you can consider retiring the powered exhaust and going with natural ventilation. In any case the air sealing of the attic floor (ceiling below) should be done and your insulation should be at least code minimum.

Almost forgot. Attic floor area divided by 150 gives you your total NFA. With just ridge and gable vents there is not a lot of height difference and it is the height that helps to create the air flow. Gables will work with a ridge but may need a breeze to help. Unknown how well, but soffit vents can be added at any time.

Bud

Thanks for the info. I made a mistake.....the soffit covers are vinyl material. But again, they are not venting anything because the wood underneath it was never cut to allow ventilation.

So they are proposing to take off the vinyl covers, cut the wood, and reuse the same vinyl covers. I don't believe there is any metal to cut.


We just moved in the house, so not sure about moisture issues long term.

We were getting insulation and roof estimates, because both needs to be upgraded. Couple people commented we have moisture issues and others said everything is ok.

We just air-sealed yesterday and upgraded the insulation to R-49.

So bottom line, from my understanding, u(and WW above) suggest i should have the soffits cut eventually?

Thanks again.

 

[Bud9051]

Did they install baffles in every rafter channel?

With no history and some comments that you have moisture issues and lacking a history being new to you, definitely add the soffit vents.

However, nix the $800 estimate. Vinyl soffits often snap out easily. Someone then cuts some holes or slots. I used a hole saw and cut between pairs to provide longer slots at each rafter channel. Then install the perforated vinyl soffit. Even if this is a 2 story home, they will be done in half a day. Pictures will help with that opinion. Get some more bids.

Busy building season so they often bid high to make adding someone to their list worth while. You might talk to the roofing company as some get involved with trim and minor work like you need. They will also have their people and equipment on site so a couple hundred extra would be gravy.

Bud

Just wanted to add, if the roofing company insists or recommends you close off the gable vents when a ridge vent is added, don't do it. The explanation is a bit long but glad to go over it as the excuses they use are not valid. They sound good, but wrong.

 

[nemo77]

Did they install baffles in every rafter channel?

With no history and some comments that you have moisture issues and lacking a history being new to you, definitely add the soffit vents.

However, nix the $800 estimate. Vinyl soffits often snap out easily. Someone then cuts some holes or slots. I used a hole saw and cut between pairs to provide longer slots at each rafter channel. Then install the perforated vinyl soffit. Even if this is a 2 story home, they will be done in half a day. Pictures will help with that opinion. Get some more bids.

Busy building season so they often bid high to make adding someone to their list worth while. You might talk to the roofing company as some get involved with trim and minor work like you need. They will also have their people and equipment on site so a couple hundred extra would be gravy.

Bud

Just wanted to add, if the roofing company insists or recommends you close off the gable vents when a ridge vent is added, don't do it. The explanation is a bit long but glad to go over it as the excuses they use are not valid. They sound good, but wrong.

Yes I had them put a baffle in each bay. After the new roof, I should have a ridge vent, soffits and gable vents? If u have time I would like the explanation of keeping the gable vents open.

Here is the pic of my soffits:

http://tinypic.com/view.php?pic=2nvayq0&s=9

Thanks!

 

[nemo77]

 

[nemo77]

 

[Bud9051]

This project is getting easier all the time. Looks like you already have perforated soffits, just need some holes above. For the guys who work off of a ladder (not me) that is a piece of cake. Pop out 3 or 4 panels, a bunch of drilling and pop them back in. Move the ladder and repeat. One guy, 3 hours, and no materials, $300 and he has a good days pay. And you get to keep the other $500.

I've been trying to correct the roofing industry for several years and some have changed. But the problem with their reasoning for removing the gable vents is, gable vents or not, it doesn't reduce the pressure across the soffits. Air moves due to a pressure difference and a path. Leaving the gable vents in place actually increases the pressure across the soffits. All of their other arguments about short circuiting are just a smoke screen. They say air follows the path of least resistance, ya, but only if two paths have the same pressure difference pointing in the same direction. The pressure across the gable vents is pointing out.

There are reasons to close off the gable vents, rain and snow being two. but yours have been in place for years and you see not issue. besides, if a problem came up, very doubtful, later on, they can easily be covered on the inside at no cost.

Bud

 

[nemo77]

This project is getting easier all the time. Looks like you already have perforated soffits, just need some holes above. For the guys who work off of a ladder (not me) that is a piece of cake. Pop out 3 or 4 panels, a bunch of drilling and pop them back in. Move the ladder and repeat. One guy, 3 hours, and no materials, $300 and he has a good days pay. And you get to keep the other $500.

I've been trying to correct the roofing industry for several years and some have changed. But the problem with their reasoning for removing the gable vents is, gable vents or not, it doesn't reduce the pressure across the soffits. Air moves due to a pressure difference and a path. Leaving the gable vents in place actually increases the pressure across the soffits. All of their other arguments about short circuiting are just a smoke screen. They say air follows the path of least resistance, ya, but only if two paths have the same pressure difference pointing in the same direction. The pressure across the gable vents is pointing out.

There are reasons to close off the gable vents, rain and snow being two. but yours have been in place for years and you see not issue. besides, if a problem came up, very doubtful, later on, they can easily be covered on the inside at no cost.

Bud

great, thanks Bud!!

I will try give it a go this weekend.

Thanks again!