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mtk 01-15-2011 10:12 AM

insulation and sealing questions stone/brick house
Hi, my 2 story with basement colonial house was built in 1935 and it has a stone foundation & brick construction. Most of the walls are plaster and wood lathe. I have a few insulation questions:

1. The existing attic existing insulation is trashed. So I am going to remove it and put in new to R60. (maybe more than needed, but since its a small house the cost was low). I bought faced r30 for the first layer and unfaced r30 for the second. The joists in the attic are 2x6. Should I fur them out to better support the second layer of r30 and to prevent compression of the first layer, or is that unnecessary?

2. I am using baffles/chutes to allow airflow from the vented soffit into the attic. But on the gable ends of the attic there is a gap between the plaster and brick. Should I leave that gap, stuff insulation in it, or seal it with spray foam?

3. Does it make sense for me to insulate the rim in the basement? There is a gap between the plaster and the brick. What insulation should I use, if any, at the rim?

thank you

Blondesense 01-15-2011 11:54 AM

I don't have any answers for you, but I gotta feeling someone's going to ask before long: Where are you located?

gregzoll 01-15-2011 12:49 PM

Do not place faced in the attic space. The building needs to breathe, and just putting Blown insulation in the attic space is better than batt. Post a picture of the attic space, showing existing insulation, and update your location. Also, seal any gaps up in the attic space around light boxes, entrances where wires enter the attic space, and around the vent stack, and furnace flue if there is one. In my house, I found a huge gap between the brick chimney for the old Octopus furnace that I sealed with some batt insulation, and pulled back against the blown insulation. Still have a area over my front entrance that I should have placed some XPS in the space, due to only 2x4 rafter on that side, but did not do it when I had the roof open on that side when we had our placed re-roofed. You just have to attic it a bit at a time, and do not over do it.

mtk 01-15-2011 03:25 PM

I am located in Baltimore, MD.

The furnace flue goes through the chimney which is on the outside of the house and does not come through the attic.

I have already purchased the batt insulation and will not be using blown in. My question about that was if I should fur the 2x6 joists to support the second layer of insulation or if it is OK to do without.

Why do you say not to used faced insulation? I am removing the existing insulation and putting the face towards the living space, and using the unfaced insulation over top of that. This is recommended by as well as many other resources.

I already planned to seal around wires and vent pipes that penetrate into the ceiling space.

The question that I had about sealing was about the space on the gable ends between the brick and the plaster walls. Should that be left open, stuffed with the fiberglass, or sealed air tight?

Thank you.

jklingel 01-15-2011 03:25 PM

Leave the fiberglass batts at the store; they are the worst insulation on earth for an attic; too porous, and can't seal everywhere. Blow in cellulose. As mentioned, air seal as best you can prior. Ventilation is always needed over attic insulation, in a ratio range of 150:1 to 600:1, somewhere the middle being most common, reportedly. You can hardly have too much, but prevent cyclones from blowing through there. Cellulose will help prevent wind washing.

mtk 01-15-2011 03:55 PM

Thanks for the suggestions to use blown in insulation but I will be using fiberglass batt insulation. There is already blown in insulation in the attic but it's only a couple inches deep in places, up to a max of 6 inches.

I am removing that insulation because it has already caused me a big problem:

The air handler for my central air conditioning is located in the attic. There is enough airflow that some of the existing insulation gets into the drain pan for the A/C. This caused the drain line to clog. The pan has a float switch, so it shut the unit off, but it was quite a bit of effort to have to unclog that line in the hot attic in the middle of the summer.

I will forgo the benefits of blown in insulation not to have to deal with that issue again.


gregzoll 01-15-2011 03:56 PM

Batt is not really the worst, since it has its place in sound dampening, and stopping the convection process through the walls. But in this case with attics as we both know, blown is the best solution. I only used faced R-13 in my basement Sills & Rim spaces, because I needed something that I could do to stop the cold air, and was within the budget for it. Unless you fluff insulation a little for places such as the Rim joist area to help stop the convection process, you are correct on not stopping the airflow. Airflow good, choking the building from not breathing bad.

mtk 01-28-2011 06:52 AM

I'm still hoping someone can answer if I should seal the gable ends between the plaster and brick or if I should leave it open.

The reason I think it might need to stay open is to let any moisture that gets into the brick to evaporate and exit up through the roof


gregzoll 01-28-2011 07:12 AM

No, you need to leave it open. There is semi-permeable sealers to not let moisture in (ie driving rain), but allows air to pass through, but would need to be applied following directions.

ccarlisle 01-28-2011 08:30 AM

What you are doing is turning your attic into a cold space, a space that is outside your 'building envelope'...which is fine. Not the way the house was designed for way back when but fine nonetheless. However certain things must be done.

Keep the attic well ventilated; not open to birds and bats and rain coming in, but open so that it breathes. Therefore, seal the gable ends - but let air in. You've already done that same thing using the chutes around the soffits...

Insulate your air handling system; it probably already is.

IMO you don't have to furr up the 2x6s to accomodate more fibreglass insulation. fill the void up to the top of the 2x6 then lay more fibreglass perpendicularly to the first layer. You avoid the crushing you are worried about...

I'm not sure how you are handling any vapour barriers you have.

And yes, insulate the rim joist voids in your basement; that's where a lot of heat gets out. Cut out polystyrene or polyisocyanurate panels to make a snug fit then seal the joints with acoustic sealant. Add fibreglass if you want.

But air seal first, then insulate. Be that your motto with your house...

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