Cape Cod Insulation
I appologize in advance for the length and complexity of this post... This is my first post in this forum. I have searched high and low for a consistent answer to my dilemma and am turning here to hopefully shed some light on my situation....here goes.
I recently bought my first home...a 1948 Cape Code in Pittsburgh. This year's home improvement project is to add insulation. I am not handy what-so-ever, so I contacted three local insulation companies and have narrowed it down to two companies which are giving me conflicting solutions (the thrid company wasn't professional, let's just leave it at that)
Company #1 plans to blow the outside walls full of foam insulation. In the side attic space, they plan to spray foam the knee-wall space and blow in a comfort therm fiberglass product into the floor of the knee wall space to an r-39 standard. They also plan on blowing additional fiberglass insulation on top of my exisiting fiberglass insulation in my upper attic to achieve a better r0rating. Company #1 did not address additional ventilation or the sloped spaces of the roof.
This is what is causing me a headache.
Company #2 plans to blow the outside wallls full of cellulose. In the side attic space, they plan to put fiberglass batts on the knee wall and blow in additional cellulose insulation into the floor of the knee wall space. In the upper attic, they plan on blowing additional cellulose insulation on top of my existing fiberglass insulation to an r-39 value. NOW, company number two made it sound like the standard to blow the slope space of my roof full of cellulose insulation and add louver? vents to my side attics. Do I need additional ventilation in my side attic? The top attic has two gable vents and a ridge vent. The side attic does not have any sofit vents. There is an access panel leading from one of the side attics to the top attic.
With all the experience in this forum, I am hoping someone or everyone probably to help me with this decision. If anything, I am hoping to learn a little more as to make a more educated decision. Thanks again for any help.
Just about impossible to tell you what's best without being there to see it.
A few facts are that no amount of ridge venting or gable vents will do anything unless you also have soffit vents.
Just try sucking on a straw with your finger over the end of it.
Any place there is soffit venting there needs to be foam baffles installed so when they add insulation it does not block the flow of air.
Insulating that space is DIY 101 and you could save your self a ton of money by just using insulated batts.
The batts that are going over the insulation you have now over the ceiling has to be unfaced so you do not have a double vaber barrier.
The rest just gets installed with the paper toward the conditioned surface, (heated and air conditioned).
We are going to see more and more use of spray foam in a building envelope...and everyone one you talk to has a different take on whats the correct application of the materials. IF you are going to ventilate the attic area, spray foam is not a good choice (IMO) because you are creating "conditioned space" and restrict air flow as Joe stated. Shingle MFG will not warrant their materials over "un-vented " roof decks. The ones who did are back peddling now.
IF you have a roof leak it will be a long time until its discovered and structure can be compromised in the mean time.
My take on insulation, from a roofing contractors view point is, spray the walls and ventilate the attic area.
What ever course you choose, get some guarantees in writing that someone is responsible if a problem occurs. Remember a warranty is not a guarantee.
Company #2 is much more congruent with all that I have learned about insulation. I have a neighbor/friend who is a weatherization consultant/inspector... he has given me tons of advice. I have read up on it as well and, in the newer books, the authors are saying the same things that he is. That said, I will share what I have learned, which really seemed to contradict a lot of other things I've read on the internet.
I, like you, have a Cape Cod, but it was built in the 50's. However, I only live a few hours from you in NE Ohio, so our need for heat efficiency is similar.
The ventilation needs a low and a high vent. For example, in the crown of the attic, the gable vents = low and the ridge vent = high. In the knee wall space, the louver vents are not going to do much good without soffit vents, I would get some no matter what you do. You need the air to circulate, but it only needs move in that space, the entire roof should not circulate the same air. You definitely do want to insulate that slope, as well make an airtight barrier. The barrier inhibits a convection effect that happens to Cape Cod homes (this effect steals your heat in the winter!). You want to seal any areas between the temperature-controlled living space and the external air.
I need to redo my attic too. My problem is that the slope has R-11 with kraft paper on both sides of the batting, so I cannot just spray in cellulose on top because of the double vapor barrier (which could encourage mold). I am going to redo the drywall on the slopes anyhow and seal it (where the slope meets the knee wall)and use newer, thicker batting. Hopefully your slopes will allow you (or them or whoever) to simply pack them up with blow-in cellulose.
Word to the wise, if you plan on redoing any electrical wire in the exterior walls, do it before you fill them with insulation. Me, I don't have any insulation at all in my exterior walls, but that is OK because I want to swap out the fabric-coated wire for grounded romex first anyhow.
You can do all this stuff yourself and save a bunch, but it will take time and effort, so it seems a compromise as to what is valuable to you. I found a site that has some good info you might want to read up on:
Welcome To Home Energy Magazine Online
I beleive convection heat on the slopes will be made worse if you fill the area with insulation. If it were my house I would remove the drywall in that area and make the rafters deep enough to take the required insulation and 2" for airflo. In the summer the convection heat will help drive the airflo from the soffits to the upper vents, this airflo will make your roof last longer. I want air to move from soffit to ridge and would not have a gable vent in the mix.
If there lots of cap house in your area talk to other owners and look at their roofs.
Tommy, I suggest you do some research, maybe even get an inspection from a weatherization consultant not affiliated with a commercial insulation company. I am just a home improvement novice, but the info I presented to you came directly from a certified county inspector who went to school for what he does, which is access water damage and weather efficiency.
P.S. Batting insulation alone does not prevent convection, air can move right through it easily. Sealing a portal with spray foam and a barrier (foam board, garbage bags full of crumpled newspaper, etc.) to where it is air-tight is truly sealing it.
In new home construction the distance between drywall and roof sheeting is 10" or more to allow for insulation and air flow, that's why I suggested lowering the ceiling in the sloped area.
I can understand you wanting some decent insulation, the weather in Pittsburgh can be cold and wet, and hot and wet.
The solutions that company number one offers are if done correctly the best you can get, (working within the existing frame.)
Four inches of sprayed in foam will provide an air tight, warmer home. (but, read lower down)
However, this will be very expensive and I wonder if in fact they can do it, using poured in expanding foam is time consuming as it creates a lot of heat when expanding, and there is the problem of how do you fill the top three inches where most of your heat will escape.
Taking the sidings off, or the drywall off to spray between the sticks is the best you can get, but I wonder it they really mean to do what you write.
If they do spray and completely fill the spaces, then there will be a lot of waste.....
and then you are left with the problem, a typical home has 1/8th of the walls, ceilings and floors made of solid wood, wood is not a good insulation, having good insulation in the gaps is all very well, but that still leaves the heat escaping through the wood.
The wood needs to be covered by sheets of polystyrene that are at least three inches thick.
I would strongly suggest that you get their specification in writing and that you watch them do the work, as I do not believe they will complete the work as you describe.
I was talking with my inspector friend and have another thought about this worth a mention... if there are currently no soffit vents, then why not just insulate the entire underside of the roof? You won't need ventilation that way, much like a cathedral ceiling. For areas where there is no drywall (kneewall area), kraftless batting between the roof joists and 1/2" foam board to cover it. Under drywall (slopes) kraft-backed R-30.
This, to me, seems like the easiest option, and perhaps the cheapest.
At first glance, this is a good idea.
However, you must take water vapor into account!
As you probably know, water vapor is created in the home by cooking, washing, breathing, sweating.
Water vapor once created is held in the air until it meets a cold surface, or if outside meets a patch of colder air, when it turns to rain, etc.
Indoors it heads for the nearest cold surface, which often means straight for the attic where it condenses on the underneath of the roof, possibly leading to mold and wood rot.
If you are going to insulate the roof, you must use at least 3 inch thick polystyrene, or another closed cell insulation, and you must ensure there are no holes or cracks in the polystyrene where the water vapor can gain access to the roof.
Fiberglass and cellulose and other open cell, so called insulation's should not be used as water vapor moves through these with ease and it is impossible to make an air tight surface.
After you have filled the spaces between the rafters you should then add another layer of polystyrene below the rafters to stop the water vapor from condensing on them.
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