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Insulation of pre-war house: Doable or too risky?

I bought a 1937 Tudor home. I had the misfortune of following a contractor's advice and getting rid of my steam system. No idea how well it worked since the replacement happened before I moved in. But I know now that steam is the best heating. I scrapped a plan for HVAC and decided to go with hot water heating (under the floor staple up radiant and cast ray recessed rads upstairs - all the emitters were formerly cabinet convectors).

this past winter was my first in the house. The hot water system on the second floor didn't get warm enough on the extreme cold days (under 20 degrees F).

I have had 2 energy audits. Both companies said it was imperative to add insulation. Attic can be done relatively easily. But the outside walls I am troubled with. These are plaster walls with little insulation now. There are a lot of comments and articles that say stay away from cellulose blown in insulation. Issues include moisture accumulation and eventual sagging of the insulation. But both energy contractors are telling me that this won't happen. they will pack in the insulation tight so it can't drop. But what about the moisture accumulation? Bob yapp has a blog that talks about these perils and eventual termites from the moist insulation.

Has anyone here blown in insulation into a very old house and not had issues for at least a few years? Any advice would be appreciated. I already got screwed from following the first contractor's advice. I can't afford to be uninformed again.

Re: Insulation of pre-war house: Doable or too risky?

Both contractors are right, however, unless you do something to provide a vapor barrier, you will have problems down the road, but this applies to any insulation you choose to use except closed cell foam. You can provide a vapor barrier by using a vapor barrier primer on all the interior side of the exterior walls and seal up all the outlets or any other penetrations in those walls, or use a vinyl wall paper.

That is the cheapest way of insulating to exterior walls, but not the best, and even it may not be worth doing. An uninsulated wall built in your home's era typically has an R-5 value. You have a relatively dead air space in the cavity plus the sheathing. If you have a brick exterior, or a lap exterior with an underlayment under the laps siding, then you have R-5. If you have no underlayment under the siding or a stucco exterior, then you have about an R-4.

Blowing in cellulose theoretically should give you an R-11, but it doesn't. 10-15% of your wall is studs which have only an R-5. Lets say 10% for now so that is (R5 x .1 + R11 x .9)=R-10.4. Actually it will be less because of jack studs and headers, etc.

Walls typically account for about 20% of the total heat loss for the house. Upgrading this way will save about half of that 20% so you are looking at a total improvement of around 10%. Now compare your actual heating bills to the estimates for the insulation to figure your ROI (payback).

Windows and doors account for about 20% as well. Going from single pane to double pane glass will save you another 10% as well, but windows are an expensive upgrade as well. Infiltration around windows and doors can cost you another 20% and upgrading the weatherstripping is often very reasonable so it should be the very first thing you do. Again you are looking at a 10% reduction of your heating bill, but the payback is usually very quick.

Now for the attic. That usually accounts for 30% of the heat loss of a house, and most of that loss will be felt on the second floor. An uninsulated attic would have an R-1. There is no dead air space above the ceiling so any heat loss to the attic goes right out the attic vents. The 30% is based on there being a couple inches of insulation up there. Even back then, a little insulation was put in the attic so the builder could save money on the size of the heating system they had to install. You probably have attic floor boards as well as they were pretty typical back then. So the current attic total should be around R-7

Upgrading the Attic to R-30 would cut the heat loss through the attic by a little more than 75%. That would save you about 23% on your total heating bill, probably a little less as you rarely achieve the stated R-value, especially if you put the attic floor boards back down.

But doing the attic is also relatively cheap and has a quick payback, and it will help to keep the second floor significantly warmer.

I'd recommend the weatherstripping first, then the attic. Go through another winter and then determine if you need more insulation. A cheap trick you can do for the upstairs windows is to make a frame out of 1x1 that fits inside the window opening with a little clearance all around. Cover the frame on both sides with clear vinyl. Put weatherstripping around the edges and pressure fit it into the window opening on the interior side of the window. It is cheap to make and cuts the heat loss through a single pane window by 70% or more. You just need a place to store them in the summer. This would be a project for mid winter if insulating the attic turns out to not be quite enough to make the upstairs comfortable,

Re: Insulation of pre-war house: Doable or too risky?

Keith you are awesome!! This is extremely helpful.

When I had the new heating system put in, I did get to see the interior of the walls as the pex was being run up from the basement. It’s not an empty cavity. Between plumbing, existing insulation (older gray type which looked pretty old), it didn’t seem like there was a ton of room in there. There was also wood chips in there. So the plumber had to either run the pex through the old steel pipes or weave it through the wall. It was an absolute nightmare. So the walls have a lot going on.

I have a stucco exterior, so I’m going to assume I have an R4 on the walls. The walls were definitely cold to touch. Sounds like the best I can get up to is R-9. Does that mean that I would halve the heat loss through the exterior walls going R-4 to R-9?

At this point, I can deal with the higher bills. I was running about $300 per month in the dead on winter in Long Island. I didn’t think that was too bad. So saving an extra 20% on bills is nice but it will take a long time to see a return on the insulation cost which is many thousands of dollars.

My windows are the original single pane and rusted in very bad shape. So I’d rather put any money into those so I can use the windows and increase the home value. For the winter I had to board them up with tape, plastic and Styrofoam. But no doubt, the comfort was increased.

You are spot on about my attic. It has attic floor boards and 4 inches of the old insulation. I added bat insulation to the roof joists. Can I add insulation to the floor as DIY project? HomeDepot rents out the blowers. The contractor pricing is several thousands of dollars.

I love your idea of DIY interior windows. I was looking at some companies who make these but it’s not cheap and adds no home value.

Thank you immensely!!! This is the best advice I have gotten. I’m going to skip the wall insulation. Do the weatherstripping and other air sealing. Then do attic and finally make my own storm windows and try out another winter.

You rock! Thank you so much.

Re: Insulation of pre-war house: Doable or too risky?

"I added bat insulation to the roof joists. Can I add insulation to the floor as DIY project? HomeDepot rents out the blowers. The contractor pricing is several thousands of dollars."

I hope by roof joists, you mean the attic floor and not between the roof rafters. Which floor are you talking about?

Re: Insulation of pre-war house: Doable or too risky?

I am probably not using the right terms. I meant I put bat insulation in the slopes of the ceiling.

Pictures are here: https://housetudor.shutterfly.com/pictures/11

Re: Insulation of pre-war house: Doable or too risky?

From what I can see so far, the insulation between the rafters isn't helping you at all as you are venting the attic space. There is little or no temperature difference from one side of the insulation to the other. The only reason to insulate the rafters and gable walls is to convert the space into living space. To insulate that space and not use it as living space means higher heating costs for no good reason.

You have a very steeply pitched roof so that means to insulate the between the rafters, you have 2 sq feet or more of surface to insulate for every sq ft of attic floor. For a given level of insulation, your losses are two or more times higher.

If you feel the need to insulate and heat the attic, then you first need to have ventilation between the insulation and the roof sheathing (roof decking). If you don't, you will shorten the life of your shingles and can cause rot issues with the rafters. The best way to vent this is to have a ridge vent installed along the peak of the roof and continuous soffit vents under each soffit. Then the insulation needs to be taken down and reinstalled with the wings stapled to the bottom edges of the rafters instead of the sides as they are now. This will give you a gap for air to flow from the soffit to the ridge. The gable vents will need to be removed and the whole wall insulated the same way as the rafters. You will need some type of drywall to hold the insulation in place.

I am guessing that your house has a part of the roof that also serves as a slanted wall for the second floor and that you have several dormers set into the roof for windows. The insulation needs to be installed in these sections just as I have described for the attic. I would also recommend a 1/2 or 3/4" thick foam boards between the rafters and the drywall. This will stop the heat path through the rafters to the roof and do away with those snow lines on the roof. That is where you can see where each rafter is by the melted lines in the snow on the roof.

You probably also have a knee wall and traditionally the knee wall is insulated and the floor of the knee wall area is insulated. If you like, you could extend the insulation down the rafters to the soffit area and cover it with the foam instead of insulating the knee wall itself. Then you could put cabinet doors in the knee wall and use that space for knic knak storage.

I would however, not insulate the top attic like you did. I would remove the attic floor boards and pile all the insulation in between and over the tops of the joists and leave the rafters and gable walls above the attic floor uninsulated.

Re: Insulation of pre-war house: Doable or too risky?

Keith - not sure if you're still out there. But if you are -- with the energy improvements, my primary goal is to get the house to be warmer. Heating bills are secondary. I don't care to heat the attic.

Would you mind telling me the recommendation on what to do with the attic that I could do myself. i do have 2 kneewalls.

i understand that the insulation in the roof slope isn't doing anything. Is that hurting the roof?

Again, I don't want to heat the attic. I just need to prevent the heatloss so the rest of the house is warmer.

I'm hoping this doesn't require removing the floorboards (which I assume is the attic floor).

Re: Insulation of pre-war house: Doable or too risky?

I'm still here. The insulation that is installed in the rafters above the rafter floors is doing more harm than good. It looks like it is pushed up against the roof decking and that will cause the shingles to get hotter in the summer. Also, the gable vents are still open so this is like putting a lot of insulation in your walls and then leaving both the front a back door wide open all winter.

I would take all this down, but keep it. Now you have cavities in the roof below the attic floor. This is the slanted portion of the walls in the room below. These cavities should be insulated, but the insulation can touch the interior wall, probably lath and plaster, but needs a 2" gap between it and the roof decking.

If there is no insulation in these cavities, you have a couple of choices. One is to remove the wall board (lath and plaster) and insulate and then replace the wall board with sheetrock. Another would be to pull the batts removed from the rafters into this space. Put the vapor barrier against the inside and use a 1x2 or 1x3 to push the insulation down into the cavity. When you can reach it from the knee wall cavity below, then pull it into place. Use small boards to pat the insulation against the inside and make the gap on the outside.

Now in the kneewall cavity, you have two choices. The conventional method is to insulate the kneewall itself and the kneewall cavity floor. Now this is where I would (and did) stray from conventional. My second floor is the same as yours with the small attic above, slanted walls and kneewalls. I continued the insulation down the rafters but with the paper stapled to the edges of the rafters and to the inside edge of the top plate of the exterior wall. This gave me a continuous gap all the way from the soffit to the attic. This insulates the knee wall cavity, but it uses less insulation than doing the knee wall and the floor. In other words, its insulating on side of a triangle instead of two sides.

In your attic, I would take up the floor boards and fill the cavities with the remaining insulation. Remove the craft paper from the insulation. If you want to get real ambitious, take up the existing insulation if it is loose fill, Lay down the remaining insulation from the rafters, or new insulation batts with the paper on and against the ceiling below, then put the loose fill over it. Fill up to the tops of the joists or more. If you stop at the top of the joists, then you can put the floor boards back down.

To recap, you would have insulation on the attic floor, down the rafters over the slanted wall below and then either down the rafters to the soffit or down the knee wall and across the kneewall floor.

Edit: adding links





Here is one site that shows my way as an alternative.


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