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acoustic58
attic insulation
acoustic58

I am trying to do my best to not relive the nightmare of last winter's ice dam issues. I have talked to a number of people and researched this topic endlessly. I understand the concept that if the attic space is close to the same temperature as the outside, this would eliminate the problem because it's the warm attic that is creating all of this. The most common answers to this issue is to make sure that the warm air from the living space is not getting into the attic, which is done through insulation. There also needs to be a ridge vent and soffit ventilation in place to keep the attic cold. One of my problems was that my house was built in 1983 and soffit vents were never installed. That will be done before winter. I also want to make sure that I have the correct amount of attic floor insulation in place. My concern is that I use my attic for storage and floor insulation is not supposed to be compressed. Has anyone been in this situation before and what was your solution. Thank you..

dj1
Re: attic insulation
dj1

Attic floor insulation should fill the cavities between the joists fully. I assume that you want to lay plywood on top of the joists, if you use the attic for storage, so the plywood should sit flat without compressing the insulation.

keith3267
Re: attic insulation
keith3267

Is your roof framing made up of engineered trusses, all 2x4's with metal plates holding them together or is it more conventional?

If it is engineered trusses, you should not be using it for storage.

You may not need the soffit vents if you have adequate gable vents. Your gable vents should have 1 square foot of vent for every 180 square feet of attic space and there should be at least two of them, one on each end of the house. If you have an 900 square foot attic, you should have a minimum of two vents each measuring 2.5 square feet, and you need at least R-19 in the attic.

acoustic58
Re: attic insulation
acoustic58

I have a reg colonial with conventional framing. This house was built in 83 and back then the idea was to seal up everything and not let any air into the house and that included the attic. About 6 years ago I had a new roof put on and during that time I had them install a ridge vent. There are no other vents into that attic which is where the soffit vents come into pay, which seem to be standard in every house made now. Both contractors that I spoke to wanted to run it the length of the house for added air flow. It was made very clear to me for that the soffit vents to work, I need to make sure there is no insulation blocking them.

I would like to put plywood down so i can use the attic for storage but I am confused because every video I see, including on This Old House, shows attic insulation above the joists. Not sure how to put plywood down and not compress it.

keith3267
Re: attic insulation
keith3267

How deep are your ceiling joists? Many are as small as 2x6, which is only 5.5" deep. R-19 is 6.25" deep so it would naturally rise above the joists.

Do you have rooms between the rafters? Those would mean you have a smaller attic, but you would also have knee walls with storage space behind them and slanted sections of you walls above the knee walls. This affects how you will do your insulation.

Since you don't have gable vents, how you do your soffit vents will depend on how the soffits are constructed. If the soffits have a triangular cavity outboard of the walls, a continuous cavity is not needed. You could use a hole saw to drill 3 or 4" diameter holes every 6 feet or so and cover them with a screened cover. You can also take down the bottom piece of plywood or whatever is used and cut it in half, cut a little more off one of the pieces and reinstall with a continuous soffit vent between the pieces.

There is also a soffit board made with a lot of holes drilled in it to replace the current piece. Just replace the current piece with this, just paint first ad try not to plug all the holes when you paint.

If you have rooms between the rafters, you have to make sure the cavity in the slanted wall has an air gap between the insulation and the underside of the roof so air will flow from the knee wall to the attic.

keith3267
Re: attic insulation
keith3267

Do a complete attic inspection, particularly around any vent pipes that come up through the attic. Often there are large uninsulated gaps in the ceiling around these pipes and a lot of warm air escapes through these. In some cases, a wet wall is installed, that is a wall with two frames separated by 4 or 5 inches in which all the plumbing is run. If you have one of these, you need to cover it with a board and insulate over it. The vent pipes will come up through these so you do have to make holes, but seal them well.

After you make or install your soffit vents, you need to make sure that the insulation in the attic does not reach all the way to the underside of the roof along the edges above the soffits. If you have to, cut a little slant i the insulation to insure air flow.

Now I am going to tell you something that goes against the grain. If you have 2x6 ceiling joists in the attic and are using R-19 insulation, if you put plywood over the joists, it will compress the insulation a little, but the loss in R-value will be only about 1, so you will end up with an R-18 instead of R-19. If you use 3/4 plywood, you will get about half of that back (R18.5). In the long run, the change is insignificant.

The biggest problem with attics is inconsistency in the insulation. Those holes for plumbing vents, if not sealed will cause a far greater heat loss (and increase in attic temperature) than a small compression of the insulation. Hold your hand over one of these gaps in winter and you can feel the warm air gushing up through the gap, almost like it is being forced up by a fan. You can loose more heat through one or two of these holes than all the rest of the attic combined.

In addition to the plumbing vents, look for the electrical boxes for the ceiling lights and make sure there are no gaps in the insulation around them. If you have recessed lights in the ceiling, you may need to make and insulated box around them, just make sure the box has the proper clearances so you don't start a fire, or just get rid of them or replace them with modern LED recessed lights that run much cooler and insulate around them.

If you feel you need more than R-19, you could (if you have the room) bring more 2x6's up to the attic ad lay them vertically and perpendicular to the attic joists. You will need to put in some solid bridging every 6 or 8 feet to keep the new boards from falling over. Then fill those cavities with more R-19 and cover with plywood. This should yield a total R-35 or so. It would be a lot of work and cost more than just blowing fiberglass or cellulose over the existing ceiling, but that is one option to having good insulation and an attic floor too.

keith3267
Re: attic insulation
keith3267

One more thing, if you have a gas or oil fired heater in your house, you may find there is a opening above the heater closet to the attic. You need to have this opening as it provides fresh air to the burner of your heater. Without it, you would burn up your warm house air. Not good.

The vent for the heater runs through the attic and it will be hot, so it will add some heat to the attic. There are some things you can do. First is to have an insulated or triple wall type vent installed. Next is to insulate the walls of your heater cabinet and weatherstrip the door. You do not need insulation with the vapor barrier for this, just plain batts will do.

If you have a gas fired water heater inside the house envelope, you need to do the same for it, although in most cases both will be in the same cabinet/closet. If these are in the garage with the doors facing the garage, then you don't need to do all this, only if they are inside the insulated envelope of the house.

You may also have a chimney and the vents for the heater and water heater may use separate flues inside it for venting. That solves some of the issues, but look for gaps between the chimney and the ceiling, a lot of heat is lost here as well. Make sure if you insulate this gap that you use high temperature fiberglass or rockwool.

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