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Chokingdogs 10-27-2012 02:26 PM

Attic insulation / venting of 60s era house
Yet another one of those posts.....I did search and look prior to posting and found some answers/advice, but not everything I'm looking for.

About to buy a house made in 1960, located for lack of a better landmark, in Gettysburg PA, so it's in that climate range. It's a 1 and 1/2 story Cape Cod "style" dormers, the front roof is one solid wall from eave to ridgeline, not sure of the angle, say 45*. From the ridgeline back, the angle is much shallower, say 15*, as all the upstairs rooms are 4 vertical walls with no knee walls. There are two rooms with knee walls front/back, but those are over the garage and the dining room, not part of my situation with the attic.

The insulation in the house is all original, and I have no idea what it is. What I can see in the forward attic/crawlspace, under the main front roof section attached to the rafters, appears to be kraft faced cellulose stuff stapled between the rafters. The paper looks almost like tar paper, only thin, think a brown paper grocery bag hit with some black spray paint.

The attic space over the rooms upstairs has no insulation between the rafters, just the same kind of black paper backed cellulose stuff between the ceiling joists, only instead of looking like R19 fiberglass, it's about an inch and a half thick laying flat on gypsum ceiling boards.

Roof/eaves have no soffit vents of any kind, nor does it have a ridge vent. The only attic venting is done through two gable vents at either end, and those are about 18" X 12". The house has hydronic baseboard heat, so I have no ductwork to worry about, no recessed lights, only a single ceiling mounted flush light in two rooms. The bathroom has nothing in the ceiling, but that will be remedied with an exhaust fan. Spacing of all joists/rafters is 16" OC, and I'm 99% sure they're all 2X4s. Slight chance of 2X6s, but I highly doubt it.

What I'm dealing with comes to around 625 sq ft of horizontal surface area needing coverage. I've decided on blown in cellulose as the insulation to put up there, I just don't want to deal with the foam stuff..... I assume I need to put in soffit vents, any recs on what type and how many? My current house has the 3" or so diameter louvered aluminum jobs spaced about every 3 to 4 feet.

Would those foam rafter vent jobs be advisable once I put soffit vents in? I assume, since the space isn't conditioned, that insulation against the roof sheathing isn't needed/required? As for building a bulkhead/dam at the eaves, would the rigid foam insulation, say 3/4" thick cut to fit, be appropriate? Should I remove what's currently up there in terms of insulation, or just leave it be and blow the stuff right on top?

Also, the house has a total southern exposure, and April through September from 9 AM to 5 PM, the sun just beats down on the front roof section. The "attic" knee walled closet area gets so bloody hot, one could almost spontaneously combust walking into it, LOL. Lastly, if it makes a difference, the house is plaster on top of 1/2" gypsum board, walls/ceilings.


Gary in WA 10-28-2012 07:08 PM

Be careful using blown-in on the low-slope section without good air movement above it;

Find the closest big City below the map for your Zone:

Find the insulation requirements needed:

Furr down the rafters on the sloped section to meet minimum or add inside rigid foamboard. Air-seal the attic floor and the drywall. Block air movement under the knee wall. Add a housewrap over the new knee wall insulation on attic side to prevent wind-washing. Add baffles of f.b to create an air channel (no insulation touches roof sheathing);

Figure NFVA:

The 3" soffit vents require 2 holes for getting the minimum 1/150 or per foot;

PS. welcome to the forums!

Chokingdogs 10-31-2012 12:54 PM

1 Attachment(s)
Thanks for the reply, and the welcome. I cannot believe I never found this site in the past, lots of great info here, and would have saved me many many instances of measuring once and cutting four times....LOL

The closest "big" cities south are, basically, Bal'mer, Frederick, and Hagerstown. All three of which are in the next zone down. Harrisburg, about 40 miles north, would that be a better measuring stick for R insulation requirements as it's in the same zone? I figure it wont hurt to go a little more than what's "required"?

I'm going to try and attach my best attempt at a MS Paint Picasso of what I have to work with. It's only a rendering of the second floor cross section, I didn't bother with the first floor. My biggest question is what to do from point A to point B - rafter vents, then a layer of paper backed insulation over top? The area marked "attic / storage", while not conditioned, is accessible off the upstairs hallway by a standard 32" X 6 1/2" doorway, and it runs from one end of the house to the other. The area shaded blue I have no idea what's there, and below that is conditioned living space.

Thanks again for any advice / guidance. I've got another, related question, that I'll post next as to not cross contaminate both situations.

Chokingdogs 10-31-2012 01:10 PM

2nd related insulation question.

House has a semi-detached garage with "living space" over it. Was used for storage, then 20 some odd years ago converted. It's accessed off the end bedroom through a standard doorway and it has retrofitted electric baseboard heat. We used to call it The Microwave, due to the fact in the summer you could put a slab of prime rib on a plate in there and after a couple'd have some nice roast beef.

Currently has rafter insulation, but I have no idea on what's behind the knee walls and under the subfloor. All I know is, in the summer it's bloody hot and in the winter one could make popsicles. There's a small peak - the "attic" - in which there's three or four bricks left out on the end to vent it. So no true gable vent, just a few holes. I plan to yank out what's currently there and drywall the whole joint. If rafters are 2X4s, should they be furred down to allow for rafter vents+insulation, or should I just insulate w/o those vents? No living space below, just the garage, but I do plan to heat that with one of those ceiling mounted electric this -

Gary in WA 11-02-2012 10:32 PM

The rafter baffles only need to be used near the soffit intake vents, unless a full cathedral ceiling. You need to establish where you want/need the insulation barrier (through the smaller attics). If going for for a vented attic, be serious about it;


Chokingdogs 11-07-2012 12:08 PM

Thanks. I'm getting quite serious about venting/properly insulating the whole shebang, especially after poking around it again this past weekend.

The "insulation", and I use that term loosely, visible in the attic/storage space in the drawing above, is this stuff:

Balsam Wool - says right on it. Made by the Wood Conversion Company, with an "average applied thickness of 1 inch", and "meets commercial standards 160-49".

The stuff is literally two pieces of black paper surrounding about an inch and a half thick mess of ground up whatever. The stuff is stapled between the rafters, with an air gap between it and the roof sheathing, from the front soffit all the way up to the attic space. I have no idea what's beneath it, the area I shaded blue above, on the ceiling above the first floor living space. That space is probably a good 8 feet deep and runs the entire length of the main part of the house, and for all I know, there's nothing.

That same stuff is what's laid between the joists in the attic, directly on top of the second floor ceiling gypsum, and why it only looked like an inch of insulation initially, because that's exactly what it is, LOL.

The roof does in fact have a ridge vent, a brighter flashlight shed more light on the subject, and viola....there one was. It's the "brillo-pad style" ridge vent.

So, plan now is - rip out knee wall in attic/storage space and existing rafter insulation, add rafter vents from soffit up to true attic, add soffit vents on front of house and baffles, then blow in cellulose to proper R value in that area. Close up knee wall.

For the actual attic, same thing sort of, rafter vents at soffit on rear of house, baffles, then blow in cellulose to proper R value in attic. There is a chimney going through the middle of the attic, it's cinderblock, and that chimney handles the fireplace in the living room below as well as a fireplace in the basement, along with the exhaust for a gas hot water heater and the gas fired boiler. Does that pose an issue with blowing in cellulose - a barrier of some sort needed, or can it be blown right against the blocks without concern?


Gary in WA 11-11-2012 09:32 PM

You need a metal barrier around the chimney, treat it same as a flue pipe. pp.6:

The brillo pad ridge vents are the worst, make sure it is not compressed at the hold-down fasteners;

The baffled ones are best:


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