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-   -   Blocked Attic Soffit Vents on North Side - How to Improve Venting (http://www.diychatroom.com/f9/blocked-attic-soffit-vents-north-side-how-improve-venting-20615/)

Jes 05-04-2008 03:29 PM

Blocked Attic Soffit Vents on North Side - How to Improve Venting
 
We have a 1970's brick ranch purchased about 5 years ago, front facing south, back facing north, front is 1 story high, back is 2 story located in Waynesboro, VA (Shenadoah Valley). Roof pitch is 3/4 (rise 3, run 4) or less - very easy to walk on.

Poor A/C performance in summer (A/C pressures OK). Was in attic last week (electrical) and noticed that the north side soffit vents were tightly plugged with insulation bats - looks like it was built that way. Soffit vents (10) in front are in every third space (24") except no vents for about 4 spaces in the center (???). Can clearly see light through the front vented spaces.

End gable vents are square openings about 2 ft acrossnear peak. No other venting.

Will probably need a roof in another 5 or 6 years and want to install a ridge vent then.

What would be the best way(s) to improve attic venting?

All suggestions appreciated - thanks.

Jes

Ed the Roofer 05-05-2008 10:39 AM

If within your budget, you should increase the amount of intake ventilation and ensure that the current vented panels and any new ones installed are not blocked by insulation. A better and more functional configuration for the soffit panels on the eave overhangs, is to install 1000 % continuous vented panels there.

If you install a new ridge vent, the best brand on the market currently, is the Shingle Vent II, from Air Vent Corp., which would also require you to block off the gable vents to prevent the short circuiting of the internal attic air flow.

Ed

Jes 05-05-2008 08:38 PM

Thanks for the reply Ed and suggested ridge vent. Iíve made some measurements and calculated the following.

The house is 33í x 65í. Attic floor area = 2145 sqft. More accurate roof pitch is 4/12.

Per the 150 sqft rule, required attic vent area = 2145/150 = 14.3 sqft total. Splitting this
60/40% for soffit and gable requires: Soffit = 8.6 sqft and Gable or Ridge = 5.7 sqft

Front vents measure 8 x 16 inches. Assuming 50% free area gives 0.9 sqft / vent giving about 9 sqft (10 vents existing, 1 every 3rd space with several spaces skipped).

In the front soffit there is a 2 x 6 spacer between trusses (spaced 24" centers) which limits air flow to about 3-1/2 inch between the roof and top of the 2 x 6. Air can flow into the adjacent spaces through the trusses.

On the back side of house I have a 20í deck where I can install vents if I remove the soffit insulation. This will allow about 10 vents or 9 sqft free vent area for 100% venting over the deck.

I estimate the octagonal gable vent openings about 2.5 bricks wide (20") giving an area of 1.7 sqft per vent. They have wooden slats and Iím guessing about 50% free area for a total of 1.7sqft for both vents.

Do my calculations seem reasonable?

Based on the above it seems that the outlet vent area is severely limited and although the soffit venting is not ideal it is about adequate but more is needed particularly on the back side.

Based on this new information what do you recommend?

Where should I look locally for the Shingle Vent II? What is the approximate cost of the vent and what should installation cost?

Should I consider power venting until a ridge vent is installed? One end or both?

Thanks for your time and expertise.
Jes

Ed the Roofer 05-05-2008 11:21 PM

Quote:

Originally Posted by Jes (Post 121201)

Attic floor area = 2145 sqft.

2145/150 = 14.3 sqft total.

Splitting this 60/40% for soffit and gable requires: Soffit = 8.6 sqft and Gable or Ridge = 5.7 sqft

Yes to all of this so far.



Front vents measure 8 x 16 inches. Assuming 50% free area gives 0.9 sqft / vent giving about 9 sqft (10 vents existing, 1 every 3rd space with several spaces skipped).

The 8" x 16" only provide 56 sq in each, per Air Vents chart on intake vents.

In the front soffit there is a 2 x 6 spacer between trusses (spaced 24" centers) which limits air flow to about 3-1/2 inch between the roof and top of the 2 x 6. Air can flow into the adjacent spaces through the trusses.

Okay, thats good.

On the back side of house I have a 20í deck where I can install vents if I remove the soffit insulation. This will allow about 10 vents or 9 sqft free vent area for 100% venting over the deck.

10 vents x 56 square inches = 560 square inches. 560 / 144 = 3.88 square feet, Not almost 9 square feet.

I estimate the octagonal gable vent openings about 2.5 bricks wide (20") giving an area of 1.7 sqft per vent. They have wooden slats and Iím guessing about 50% free area for a total of 1.7sqft for both vents.

You have to check for a similar style and size from a Gable Vent manufacturer to see what that size is rated for.

Do my calculations seem reasonable?

Your math, or maybe mine, since its late, is off.

Based on the above it seems that the outlet vent area is severely limited and although the soffit venting is not ideal it is about adequate but more is needed particularly on the back side.

Based on this new information what do you recommend?

Where should I look locally for the Shingle Vent II? What is the approximate cost of the vent and what should installation cost?

ABC Supply, Bradco, Allied Building Materials, Shelter Distributing, West Roofing Supplies, or any local Roofing Supply House or contact Air Vent at 1 (800) Air-Vent to see the closest dealer near you. Costs vary around the country. It costs Me about $ 3.00 per foot, sold in 4 foot sections, so just under $ 12.00 per piece.

Should I consider power venting until a ridge vent is installed? One end or both?

How long will this be for?

Thanks for your time and expertise.
Jes

You are welcome, Jes.

Ed

the roofing god 05-06-2008 12:18 AM

WHERE THE SOFFIT/OVERHANG JUNCTURES ARE PLUGGED,YOU MIGHT TRY PUSHING THRU SOME 2-3 "SECTIONS OF PVC PIPING TO CONTACT YOUR VENTING,PUT AS MANY PIECES AS NECESSARY(sorry caps)

Jes 05-06-2008 09:35 AM

Thanks guys.

I'll look for some scrap PVC pieces. Don't know how tight the insulation is. It may come out easily and if that's the case I won't need the PVC.

And I'll check my math later Ed - I just guessed at a 50% free area factor but may have neglected to use it?

Thanks

Jes


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