How to insulate the roof of a ~70-year old home?

[rivan]

My house was built in the early 40s and there's very little attic over most of the second floor (only over the middle ~12-15 feet or so). The bulk of the ceiling/roof is whatever the thickness of the joists are. The roof is newer (less than 10 years old) and the ceilings are plaster/lathe. As far as I know, the roof isn't insulated at all.

I'm looking at getting insulation in there - what are my options?

 

[TwiceOver]

Probably that spray in expando foam stuff. They drill a hole at the top of the ceiling cavity then pump the stuff in and it fills all of the gaps. You'll have to fix the holes that they drill in though.

Not sure what that'll do to your plaster/lathe though...

 

[OutHouse]

you never insulate the roof. it traps moisture and you will have mold in no time flat. Instead you insulate the floor of the attic.

**Disclaimer. this is what i have been told by builders and watching home improvement shows.

 

[NutBucket]

However you can add solid foam insulation above the sheathing and shingle on top of that.

 

[Possessed Freak]

Radiant barrier maybe?

 

[Imp]

you never insulate the roof. it traps moisture and you will have mold in no time flat. Instead you insulate the floor of the attic.

**Disclaimer. this is what i have been told by builders and watching home improvement shows.

This is what happened in mommy's house. Daddy randomly stuffed bags of BATT into spaces between joists, we got major condensation because the uninsulated attic was right above a washroom with shower. Wrecked the ceiling of the other room below (sloped roof, water directed away from bathroom). This is why you usually ventilate your attic too.

You could insulate a roof, you'd just have to do the math and make sure your insulation design works. That could require an engineer... It's like a 30 minute calculation if you know what you're doing. But your warm, moist air would still be getting into the attic and if you've seen a cold bottle on a hot, moist summer day, you can guess what happens.

 

[BoomerD]

Remove existing roof...rebuild...Insulate the attic when you have the top off. The roof CAN be insulated...as long as its done right.

(OR...blow insulation into the existing attic space. talk to an insulation contractor)

 

[Humpy]

My house was built in the early 40s and there's very little attic over most of the second floor (only over the middle ~12-15 feet or so). The bulk of the ceiling/roof is whatever the thickness of the joists are. The roof is newer (less than 10 years old) and the ceilings are plaster/lathe. As far as I know, the roof isn't insulated at all.

I'm looking at getting insulation in there - what are my options?

You kind of have to determine what your desired outcome is and if insulating the roof will accomplish the goal. Just getting insulation in there might not gain anything. The house was fine for 70 years why does it need to be changed now?

There are a ton of options installing either from the exterior or interior, with complete tear offs or through holes, using fibrous materials, expanding chemicals, or rigid sheets as the insulator.

Without clear goals and knowing specifics about the construction of the house and the climate where it is located, there are no real answers to be found here.

 

[BoomerD]

OK, Humpy...that's it. I'm reporting you to the mods for trying to inject some common sense into an OT thread.

 

[rivan]

You kind of have to determine what your desired outcome is and if insulating the roof will accomplish the goal. Just getting insulation in there might not gain anything. The house was fine for 70 years why does it need to be changed now?

There are a ton of options installing either from the exterior or interior, with complete tear offs or through holes, using fibrous materials, expanding chemicals, or rigid sheets as the insulator.

Without clear goals and knowing specifics about the construction of the house and the climate where it is located, there are no real answers to be found here.

My goal is lowered heating and cooling bills and a more consistent environment inside the home (it's typically 5+ degrees warmer on the second floor). Step one to figuring out if this is a project that gets done is deciding how to 'fix' my problems and step two is seeing how much it'll cost then deciding if the price tag is worth it. Of the two, it's definitely harder keeping the house cool than keeping it warm.

Why change it now? See above. All is well when the temp's between 65 and 80 and we can keep the windows open. The rest of the year we have heat or AC running and I'd like to be more efficient in its use. If insulation won't help, then I'm open to other suggestions - I've considered a second floor exhaust as well.

The home is primarily full masonry with two newer framed additions. One addition is small, about 9x12. The other is ~20x28 and has it's own climate control. The attic space above those areas are well insulated. The airflow from those areas is negligible. The windows are newer, circa 1985 Pella double pane wood.vinyl construction (the only vinyl are the sliding areas on the sides) and are in very good shape.

The second floor is dormered; where the roofline was modified for the addition, the exterior wall is some sort of painted shingle - I think a compressed fiber material.

I'm in St. Louis Missouri - hot, humid summers with typically mild winters.

 

[Fritzo]

Probably that spray in expando foam stuff. They drill a hole at the top of the ceiling cavity then pump the stuff in and it fills all of the gaps. You'll have to fix the holes that they drill in though.

Not sure what that'll do to your plaster/lathe though...

This works well. Blown insulation is another option.

 

[Red Squirrel]

You still want air circulation, so if it really is only the thickness of the joists, I'd spray foam INSIDE the house on the ceiling and then build up another ceiling over. You'd have to remove/relocate any electrical though. You don't want any junction boxes in there. You want at least R60 for a roof/ceiling. New, I'd go even higher. R80+. That's where you lose all the heat, you can never insulate too much. Well there is a point of diminishing returns but more is always better.

This is also an instance where a ridge vent makes sense, as each joist cavity is it's own air passage so it needs to have an opening for each one. If it's a cottage style roof it gets a bit more complicated. I'm not sure what is the proper way for those when it's a vaulted ceiling.

In your case the part that shows having insulation is probably empty, and since it's lathe and plaster it would be a HUGE mess to remove, so I'd just spray foam on the ceiling from inside, and then build up another ceiling. (add some new joists before insulating).

Also that will actually be better as in that pic, the junction between the roof and the wall has an insulation "dead zone" where the double top plate is. That's a huge heat loss and is typical in even modern to code construction.

 

[Mixolydian]

The house was fine for 70 years why does it need to be changed now?

Not sure if serious. :hmm:

 

[swanysto]

I am not sure what your budget is, but if you really want to do it right, tear out the plaster ceiling. Put foil paper on the underside of the joists. Then put a layer of drywall over the foil paper. Then go in the roof and lay insulation in between the floor joists, on top of the foil paper. I would suggest a 1 1/2" to 2" rigid foam(you can get at home depot. Otherwise you can lay down fiberglass or mineral wool insulation.

That will keep your air and heat in, and it will keep everything else out(at least from the roof, I can't say the same for the walls). Not to mention, drywall is much easier to work with for anything you need to do in the future. Plaster is a pain.

 

[edro]

you never insulate the roof. Instead you insulate the floor of the attic.

I agree with this.

We had new shingles put on our old 1920 house, which had an attic, but no roof vents.
They had to install 3 roof vents because the warranty info on the shingles required it.
They needed circulating air in the attic. A positive to the roof vents... it doesn't get nearly as hot up there now.

 

[Humpy]

My goal is lowered heating and cooling bills and a more consistent environment inside the home (it's typically 5+ degrees warmer on the second floor). Step one to figuring out if this is a project that gets done is deciding how to 'fix' my problems and step two is seeing how much it'll cost then deciding if the price tag is worth it. Of the two, it's definitely harder keeping the house cool than keeping it warm.

Why change it now? See above. All is well when the temp's between 65 and 80 and we can keep the windows open. The rest of the year we have heat or AC running and I'd like to be more efficient in its use. If insulation won't help, then I'm open to other suggestions - I've considered a second floor exhaust as well.

The home is primarily full masonry with two newer framed additions. One addition is small, about 9x12. The other is ~20x28 and has it's own climate control. The attic space above those areas are well insulated. The airflow from those areas is negligible. The windows are newer, circa 1985 Pella double pane wood.vinyl construction (the only vinyl are the sliding areas on the sides) and are in very good shape.

The second floor is dormered; where the roofline was modified for the addition, the exterior wall is some sort of painted shingle - I think a compressed fiber material.

I'm in St. Louis Missouri - hot, humid summers with typically mild winters.

Lowering energy use, increasing comfort, all at a cost that is worth it. Is that all? :biggrin: I still won't suggest specific actions other than to read the applicable documents in the link. You'll be in a excellent position to talk with contractors and analyze costs after you do.

http://www.buildingscience.com/resources/retrofits

Here is a specific paper that examines the topic with similar circumstances to yours:
http://www.buildingscience.com/docu...ion-two-advanced-weatherization-packages/view

 

[Red Squirrel]

I agree with this.

We had new shingles put on our old 1920 house, which had an attic, but no roof vents.
They had to install 3 roof vents because the warranty info on the shingles required it.
They needed circulating air in the attic. A positive to the roof vents... it doesn't get nearly as hot up there now.

Roof vents are also really important to prevent ice daming. What happens is without circulation the attic heats up and starts to melt the snow on the roof. Even with proper insulation, without venting it eventually warms up in the attic.

Vaulted ceilings can make all this trickier though.

 

[Humpy]

Not sure if serious. :hmm:

Like, totally super serious.

Sometimes the best thing to do with old houses is nothing.

Turning up the AC or the heat is, all things considered, usually less expensive in reality than a stand alone energy retrofits that may or may not meet expectations.

 

[Humpy]

All the stuff about venting and mold and shingle warranties is only sometimes true. Conditioned attics with unvented roofs are a common practice if, for example, there is a lot of duct work running through the attic or the attic is used for storage.

 

[Puppies04]

Depends how long you are planning on keeping the house. That expanding foam stuff works but when it eventually fails it will cost you thousands to remove as it sticks to everything it touches.

 

[EagleKeeper]

Your can blow in cellulose.

Bat insulation in the ceiling joists will work IF not foil back or foil is to outside. You do not want to trap moisture in.

Paper backed is ok for roof and floor.

recommend you contract your electric or had provider. Most have insulation programs to help defray costs and also recommend contractors. Some will do energy audits at little ,($50) to no charge.

Attic vents with air or electric fan circulation systems will help pull hot air out of the attic.

 

[Greenman]

Op, do yourself a huge favor and have a pro look at your house. The one thing you don't want to do is simply stuff those joist bays with insulation.