Need advice on renovating 60 year old home in Maryland.

[NRGarrott]

I just moved into a 60 year old 900 square ft, rambler in Maryland. I have a newer oil furnace, original drafty windows, 6 inches of old blown insulation in the attic with a tongue and grove floor above it, and no insulation in my plaster walls. I am a carpenter/roofer part time, and I am looking for some advice on how to insulate the place. It needs a new roof and siding in the spring. I am currently planning on adding a couple inches of spray foam to the underside of the roof deck, to seal everything. Then I am going to add 4 inches of rigid foam to the top of the roof deck, add plywood, and shingle it. For the walls I was planning on blowing loose pack celluse from the exterior, and then sheathing it in 2 inch rigid foam board, then wrapping that with a vapor and water resistant barrier, then vinyl siding. I'll probably replace my windows with builder grade vinyl when I re-side the place. I can't pull the floor in the attic, this house is less than 1/2 the size of our last house and my wife would kill me if I took that storage from her. It is only a 4/12 pitch so the headroom is limited as is.

 

[woodgeek]

Sounds like a major energy retrofit. You have clearly already read about the subject...

(1) The use of a vapor barrier (e.g. ice and water shield) outside foam is not recommended for your climate, maybe under the foam, but a lot of $$ for no purpose. Tyvek would be an appropriate air barrier that would allow trapped water vapor to escape. If you lapped and taped the exterior foam it would be a good air barrier, and you could worry less about a second air barrier on the outside and go with tar paper for rain shedding under the siding. Research fastener tech to avoid saggy siding...thick foam is hard, 2" or less is easy.

(2) You did not mention windows....how you flash the windows will be very important and will require your careful attention. In many similar retrofits, the windows and their framing are completely redone. The budget alternative is new low-e storm windows over the existing primary windows, if these can be mounted at the same plane as the new siding, this may provide a strategy for simpler window flashing.

(3) If you can afford to foam under the roof deck for airsealing, then that does obviate sealing the floor, and helps get the deck R-value up to the level needed (with the foam boards above). This stackup is complicated....you will want to do some research to find something that won't rot. My **guess** is that vapor impermeable foam above deck, with open cell (icynene?) underneath to dry to the conditioned interior. You would need drywall or equiv to make into a 'playroom'.

(4) Lots of details at the eaves to figure out....look up 'chainsaw retrofit' where they saw off all the existing rafters.

(5) Cellulose in the walls is a big thumbs up!

 

[woodgeek]

On a (time or money) budget, I would do the roof work (sounds like it needs to happen anyways), and blow the walls with cellulose (which also airseals the whole structure). IF the windows are in good shape, you could call it a day. If they are falling out, you could go for low-e storms and then call it a day. This way you avoid some very PITA window removal/remounting/replacement and flashing details all over the exterior.

The losses from a 2x4 cellulose wall and a 2x4 cellulose wall + 2" foam are not that different. While R-20 is a lot better than R-10, halving the heat lost out the walls might not be worth the considerable effort.

 

[NRGarrott]

Dupont recommends that a water resistant barrier be installed over the foam, because taped and sealed foam boards lose dimensional stability and can cause leaks. Why would the air barrier go under the foam in my climate? With my plaster wall I think everything would dry to the interior, and the foam would stop the warm moist air from condensing on the barrier.

I mentioned early that my windows are original, and poor quality, single pane with no storms, and very drafty. I was thinking building window bucks out of plywood and putting new builders grade vinyl windows in.

The only framing details I am really worried about are the gable ends, because I don't have any overhang. I think my best option is to cut the 1"x6" roof deck back 7 feet, and then deck it in 3/4 plywood, and cantilever the plywood 1' over the gable end. Then build a ladder frame out of 2x4s.

The cellusose I would blow in would be loose pack, because I don't want to pay a company to dense pack it. I realize this is less then ideal, but money is tight. Unless you think leaving the foam boards off, and hiring it out to be dense pack would have a greater return for my money.

Thank you for your help, I have done a lot of research but the more I read the less I feel like I know.

 

[NRGarrott]

Here is a link to DuPonts research on rigid foam as a WRB.

 

[semipro]

(1) The use of a vapor barrier (e.g. ice and water shield) outside foam is not recommended for your climate, maybe under the foam, but a lot of $$ for no purpose. Tyvek would be an appropriate air barrier that would allow trapped water vapor to escape. If you lapped and taped the exterior foam it would be a good air barrier, and you could worry less about a second air barrier on the outside and go with tar paper for rain shedding under the siding. Research fastener tech to avoid saggy siding...thick foam is hard, 2" or less is easy.
(2) You did not mention windows....how you flash the windows will be very important and will require your careful attention. In many similar retrofits, the windows and their framing are completely redone. The budget alternative is new low-e storm windows over the existing primary windows, if these can be mounted at the same plane as the new siding, this may provide a strategy for simpler window flashing.

I agree with woodgeek overall but would offer the following as a potential mod:
When adding foam to the exterior you have choices WRT to fenestration locations (inner wall, outer wall, midway). I recently read an article (that I can't seem to find right now) that suggested that the location of water/air barrier (e.g. Tyvek) be placed on the same vertical plane as fenestration (doors, windows) to allow easier/better creation of a continuous water/air barrier.
I can't recall if there were any caveats on climate zone WRT to this advice. If I come across the article I'll post the link.

 

[semipro]

The cellusose I would blow in would be loose pack, because I don't want to pay a company to dense pack it. I realize this is less then ideal, but money is tight.

Does this mean you're planning to install the cellulose yourself? If so, how were you planning to install?

 

[semipro]

Dupont recommends that a water resistant barrier be installed over the foam, because taped and sealed foam boards lose dimensional stability and can cause leaks

The Building Science folks observed this (foam shrinkage) on their office where they had done an exterior foam retrofit some years ago. They now recommend multiple thinner layers of foam with offset seams be applied rather than a single thicker layer.

 

[NRGarrott]

At a local Lowes if you buy 10 bags of cellulose, they will rent you a blower for free. Apparently these blowers work fine for loose attic insulation, but do not have the power required to pack cellulose in a wall cavity to 3.5lbs density.

What does WRT stand for? Water resistant.. ...?

 

[semipro]

The only framing details I am really worried about are the gable ends, because I don't have any overhang. I think my best option is to cut the 1"x6" roof deck back 7 feet, and then deck it in 3/4 plywood, and cantilever the plywood 1' over the gable end. Then build a ladder frame out of 2x4s.

Just to toss out another roof insulating option that might help the issue you describe above.
You could add foam above the existing roof sheathing instead of under it. This would allow you to cantilever the foam and new roof deck over the gable ends.

 

[semipro]

At a local Lowes if you buy 10 bags of cellulose, they will rent you a blower for free. Apparently these blowers work fine for loose attic insulation, but do not have the power required to pack cellulose in a wall cavity to 3.5lbs density.

What does WRT stand for? Water resistant.. ...?

WRT = "with respect to".

I've found through first hand experience that you can get a pretty tight pack with the big box blower. I found some reference to this online before I installed cellulose in some cantilevered floors at our house. With diligence, and probably depending on the machine used, I think you can pretty easily get a "medium pack".

 

[NRGarrott]

I'm glad to hear I can do a decent job with the big box blower.

I was planning on spray foam under the existing sheathing and polyiso board above. I'm not sure if I am going with closed cell or open. I think they make a type of SPF that doesn't require a thermal barrier. That will be my top choice depending on cost.

My limiting factor for everything will be cost, I wasn't expecting to put 10k immediately into this house.

 

[semipro]

My limiting factor for everything will be cost, I wasnt expecting to put 10k immediately into this house.

One thing I've found is that board foam is far cheaper than spayed foam per unit volume, at least given my local rates provided by spray foam contractors.
So, if there's anyplace you can install board foam yourself instead of spray and you're willing to put in the effort...

 

[semipro]

I was planning on spray foam under the existing sheathing and polyiso board above. I'm not sure if I am going with closed cell or open. I think they make a type of SPF that doesn't require a thermal barrier.

Sorry, I didn't realize you'd already planned to place foam above the roof deck.
This product may be of interest to you. Its a foam board with a fire rated facing.
http://building.dow.com/na/en/products/insulation/thermaxsheathing.htm

 

[NRGarrott]

I'm hoping to get away with only a couple inches of spf inside, to air seal the attic. I haven't decided on what house wrap to use, probably something that makes air sealing easy.

 

[Circus]

I wouldn't insulate the rafters if the attic is only cold storage (usually vented). Definitely fill the walls but first look inside the wall with a mirror or scope. Sixty years ago cross bracing or fire stops were common. If you have a basement, insulate and seal between the floor joists at the sill. Check that interior walls or floors don't have internal openings to unheated spaces.
Don't place a vapor barrier on the exterior. House wrap is OK. Fortunately Maryland isn't too cold. Shouldn't cost much to button things up.

 

[NRGarrott]

The ceiling is practically uninsulated so all interior heat rises through the ceiling into the attic. Why no vapor barrier on the exterior in my climate?

 

[Circus]

Why no vapor barrier on the exterior in my climate?

Soaked insulation and rot. Hmm? How much AC do you plan on?

 

[NRGarrott]

There is no interior vapor barrier in my house, so the walls will dry to the interior if they are wet for some reason.

 

[Seasoned Oak]

At a local Lowes if you buy 10 bags of cellulose, they will rent you a blower for free. Apparently these blowers work fine for loose attic insulation, but do not have the power required to pack cellulose in a wall cavity to 3.5lbs density.
. ...?

Yes very important ,wall must be packed tight to allow for settling. many people dont realize a loose packed wall can settle as much as a foot. Cellulose will relax gradually after installation and a well packed wall wont settle.

 

[Seasoned Oak]

I can't grt hyper linking to work correctly on my phone, but underneath should be a link to DuPonts research on rigid foam as a WRB.

https://www.google.com/url?sa=t&sou...4nYepJgBoVkatTUCw&sig2=q8KCpoSr-mtFRaf3V-ILjA

Sounds like a better solution would be foam under the drywall in addition to cellulose in the wall.

 

[Circus]

There is no interior vapor barrier in my house, so the walls will dry to the interior if they are wet for some reason.

In winter, damp air from inside works through the wall and would condense on the wall side of a exterior vapor barrior. Reverse in summer.

 

[NRGarrott]

I thought the cellulose and foam board would prevent the warm moist air from reaching the dew point.

 

[Circus]

I thought the cellulose and foam board would prevent the warm moist air from reaching the dew point.

It would make the vapor barrier (water barrier) colder. I'm assuming the vapor barrier is outside the insulation.

 

[NRGarrott]

Maryland is a mixed humid climate zone 4. The rigid foam board will form a vapor barrier on its own. Condensation won't form in this climate with r13 exterior foam board. The interior of the foam board won't get cold enough.