Installing Ridge Vents, Rafter Vents, And Blow-in Insulation. - Insulation - DIY Chatroom Home Improvement Forum

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Old 04-16-2019, 08:37 AM   #1
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installing ridge vents, rafter vents, and blow-in insulation.

Hi, I am new to the forum and would greatly appreciate any help or suggestions.

House was built in 1959 and is one story with brick exterior. Current situation is this,

1. one 1200 cfm elec attic fan middle of house, a gable vent on each end approx. 3' at it's widest point and no more than 12"s in height. Looks like the seller/contractor placed the vinyl soffit over the wood and there are no holes for ventilation to get heat out the attic. Furthermore the rafters that in attic/above bedrooms are only a 3-1/2' in height. Explains why in summer bedrooms are so dang hot and cannot get them to cool down any.

The two bedrooms come off side of main house. Each of the two bedrooms sit approximately 16' off each side of the house. Over the two bedrooms it has no ridge vent, no rafter vents. Most of the attic the current insulation is below the rafters and is inefficient and I need to get this done as my wife is very susceptible to the heat after recovering from Chemo treatments.

2. No part of the house has any rafter vents for pressurization or any ridge vents.

Plan is before it gets too hot to install these items below,

a. rafter vents (It takes time but was thinking of making my own out of wood and not worry about it breaking/failing over time. Not likes the plastic ones that have a 1" vent you buy from lowes or home depot. I feel I can make the rafter vents and install them.

I had seen some websites that help calculate the amount of rafter vents needed. Anyone know of a site that is better at calculating rafter vents needed for a 1,800 sq. ft. house?

Making sure that house has pressurization using rafter vents and a ridge vent should keep heat flowing and cool attic down considerably.

b. Blow-in insulation Owens Corning fiberglass using machine to blow in required amounts needed.

c. adding ridge vent to roof lines. main house and ridge over two bedrooms. When adding ridge vents does anyone add any type of ice shield or paper to keep moisture off the wood exposed from cutting opening?

I would like to get done in next three weeks as crawling inside attic will get hotter and miserable....

Thanks for any input or advice!
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Old 04-16-2019, 09:05 AM   #2
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Re: installing ridge vents, rafter vents, and blow-in insulation.

Hi Garland,

Your closest big city so we will know your climate?
1,800 sq ft of attic floor in a home of that age would want 1 ft² of NFA (net free area) for ventilation for every 150 ft ² of attic floor. That sets your ventilation target at 12 ft² total which gets divided half high and half low. NFA for most vents is approximately 50% of the apparent area, unless otherwise listed.

Passive attic ventilation does not help a lot to cool an attic, but it helps. Protection from heat comes from the insulation which you describe as insufficient. Air sealing the leaks between attic and living space can also help a lot.

Your location will tell us how much insulation you need.

Your description of the gable vents implies wide and low or a low slope roof. You need to be sure the ridge vent you install will work with that slope.

That will get you started.

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Old 04-16-2019, 09:32 AM   #3
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Re: installing ridge vents, rafter vents, and blow-in insulation.

Sounds like you have a basic ranch house with a couple gable roofs over two bedrooms.
Rafter baffles, you can make your own or use the foam egg crates. Yours will be better, but the egg crates are pretty much industry standard and widely accepted.
The last baffles I installed, I tacked 1 1/2 x 3/4 pine strips along the rafters, then covered by stappling with 1/2" foam leveling board.
You mention rafter vents multiple times in your post. I assume you mean soffit vents. Your existing soffit will need to be removed and a strip of the wood cut out. Continuous vented soffit is better than using individual vents.

Before purchasing soffit vents or ridge vents familiarize yourself with NFVA (net free vent area) of the various vents. Vents are not all created equal and there are many on the market that I would consider inferior.
But ideally, I would be looking for a soffit vent that can deliver 10+ NFVA inches per foot and a ridge vent that is double that. So around 20" per foot.

There is plenty to read on the subject with a quick search of attic ventilation.

Last comment. Blown insulation. I have used several times years ago. Now I will always pay more and use fiberglass. Typically I like to lay the first layer parallel with the ceiling joist. And then a second layer perpendicular. It gives you a even coat with little mess. The blown in is difficult to achieve a even layer. Typically makes a huge mess. And if you ever need to take out some ceiling drywall, it will all come back to greet you.
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Last edited by Yodaman; 04-16-2019 at 09:35 AM.
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Old 04-16-2019, 01:07 PM   #4
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Re: installing ridge vents, rafter vents, and blow-in insulation.

Closest Big City is Richmond Virginia 23230
I will take pictures of the soffit, roof line, and try from inside the attic. The exterior trim was wrapped in trim coil and a vinyl soffit was placed over a solid wood surface under the eaves of house.
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