Subscribe or Renew Membership Subscribe Renew

OLD HOUSE attic insulation

dennyjames's picture


We own a 110 year old farmhouse in south eastern PA, and want to convert the attic to usable living space.  There are NO SOFFIT or ROOF VENTS,  there are windows in the gables.  I want to insulate the roof rafters but have been told I'll have a condensation problem with fiberglass battts, even if I use a poly vapor barrier.  Have had quotes for both open and closed cell foam, both have good arguments.  The floor is currently "insulated" under the floor boards with a few inches of very old blown fiberglass...does this have to be removed?  One contractor says yes another no.  Can or should I add another 3 inches of fiberglass over 3 inches of closed cell foam or will this cause condensation?  Do I insulate the knee walls?  After 4 contractor bids I am more confused than ever.

Thanks Denny

It is maddening (post #207467, reply #1 of 4)

It is maddening that you ask six guys about insulation and get six different answers.  I hear you.

I think the guy saying you will have condensation problems with FG is probably off.  Millions of homes are built that way.  There will be a lot of slamming of FG here on this board, but I really don't see the condensation issue as one of them.  Although we can return to the first statement I made and be assured someone will disagree.

Many will say go with the spray foam.  I think it is very expensive.  However, since you don't ahve vents, and it is my understanding that hot roofs (those with no vents) work well with foam, it might be your best option.  Can you add vents?  What is the size of your rafters?

As for floor insulation.  I would say leave it.  However, it might make your new attic space more difficult to heat or atleast to regulate your heat.  With no insulation in the floor heat from below is "more" free or at least able to migrate to the attic and be more balanced with the rest of the house.  With insulation your heating system will have to be perfect.  Maybe that is not that hard to do.  Leaving the insulation also would give you an option to shut the space up when not using it and not heat it, and save energy and money.

Ok, just food for thought.  Now wait for six experts to give you advise.  LOL

. understatement (post #207467, reply #2 of 4)

The rafters are not standard, approx.3 1/2 inches x 6 1/2, on 24 inch centers. The roof deck is 5 years new with asbestos shingles.  Both the closed and open fcell foam quotes are very expensive.  Close to 5 K. Closed foam guys recommending 3 inches, open cell guys want to fill the cavity.  I plan to use the room as a library and play room and it it will be used primarily only on weekends. One contractor wants to blow in packed cellulose AFTER I drywall, not an option I prefer.

There is an air handler and ductwork in the attic (sitting on the roof cross braces) so HVAC will not be a problem.   One insulator (closed cell) suggested the minimal amout of floor insulation will help with noise in the bedrooms below when people are using the room, another (open cell) said it would cause a problem, but he was not specific about what the problem would be.  FIberglass batts with a poly vapor barrier would save me a fortune but  all contractors agree that without proper venting I will have a condensation problem.  I could add a ridge vent but adding soffit vents would be difficult and prohibitively expensive.  My understanding is you need both for effective ventilation.

I was thinking I would bite the financial bullet and have the 3 inch closed cell applied. That equals R21, I thought it would be good to then add 3 inches of Fiberglass to fill the cavity before putting up the DW, But the closed cell foamer said that would cause condensation, While assuring me that the 3 inches of foam, with another 3 inches of nothing but air  under the DW would not cause a problem.  This makes no sense to me.



What size (post #207467, reply #3 of 4)

are the rafters... 2 x ?

You are best off building a hot (unvented) roof with closed cell spray foam, or rigid polyiso. You might be able to get away with open cell (depending mainly on the thickness), dense pack cellulose, or fiberglass, but it's a lot less of a sure thing. A poly vapor barrier probably isn't adequate to keep humid air from leaking in, and if enough gets in your could easily have a problem.

If course, there have also been problems with closed cell in this type of installation, in cases where the foam doesn't stick well, shrinks away from the framing, forms fissures, etc. These generally seem related to very cold temperatures, incorrect mix ratios, overly thick "lifts", wet framing, etc.

If there are kneewalls, you have to decide whether to insulate them, or insulate the entire roof and the exterior walls. I would do the latter in most cases.

Old farm house (post #207467, reply #4 of 4)

I had a very similar situation. A 180 year old mill house in Upstate New York. In the 80's I had converted the attic into bedroom space. The roof joists were old growth lumber and true 2x5s so I used 3 1/2" batt insulation with a vabor barrier. It was not the warmest space. It worked ok, while fuel prices were low. Not any more!!!

This past summer I gutted the space down to the studs along with removing the floor. As you would expect in a 180 year old house, lot's of mouse holes and activity signs. New floor joists were sistered onto the old crooked floors, along with rot and decay repair. All gaps and mouse holes were sprayed with GREAT STUFF Pestblock. A 6"layer of cellulose insulation was layed down between the first floor and attic. Than Advantac subflooring was glued and screwed down. The floor now is extremely ridgid and no squeeks! The cellulose does a great job decreasing the noise transmission between floors. My wife can have the stereo going in the attic and I can't hear it down stairs.

For the roof, I contracted to have it sprayed with close cell foam. I contracted for 4" of foam, but they totally filled each bay.  Since old houses are so porous with many holes, cranies and crazy building methods, the only way to truely seal it up was with foam!

Now that we're thru most of the winter, I can truely say that the closed cell foam was a great decision! Money well spent.The house is extremely tight. No snow melt on the roof due to heat transfer. The attic bedroom is very warm and comfortable with no drafts.

As a side note, I contacted foamers in early July. Work was very slow for them at the time so they wanted to keep their crews working.They said they'd give me a very competative price just to get the work.  I was quoted a price of $1.02 per board foot for 2lb closed cell foam which I thought was a no brainer!!


Go with closed cell foam, you won't regret it!