Renovation of a historic brick duplex
My wife and I are starting the renovation of a brick duplex in a historic district in Tallahassee, FL. It has the original cement-asbestos fiber roof over tongue-and-groove decking which will remain after a few repairs.
Two heat pump units were already installed (air handlers and duct work in the attic) when we purchased the building and some cellulose insulation has been blown in the attic. We’ve had the city do an energy audit where the main comments were to add more insulation in the attic and weatherstrip the existing doors and windows.
Also recommended was to add a vapor barrier over the dirt in the crawlspace. The crawlspace has 2-3 feet of access space throughout the footprint of the building and has a brick skirt with vents. They said, “Don’t worry about insulating the floor as the payback time is too long.”
Our intent is to convert the duplex to a single-family home upon completion of the renovation. All original doors and windows will remain after intensive weatherstripping.
My first question has to do with the attic insulation. Some attic insulation is good but air handlers and duct work in an unconditioned attic is bad. My first thoughts after reading many of the posts is to extensively try and seal any air gaps between the ceiling (single story structure) and attic. There doesn’t appear to be any evidence that this was done originally. Then reseal all duct joints etc and pile on more cellulose. There are no ridge or gable vents just some in the soffit. Anything else?
The heat pumps are probably 5 years old and not very efficient I would guess. Rental units, etc. I’m not opposed to replacing them if the long term cost-effectiveness made sense.
I would consider foaming the roof sheathing from inside the attic but have read here that leaks may go undetected and with the age of the decking and shingles some leaks seem inevitable over time. Thoughts?
Not to drag this post out but a quick question about the crawlspace. I’m not sure what is accomplished by just adding a vapor barrier to a vented crawlspace. I’ve read here where the insulated crawlspace vs. insulated floors have been discussed. I asked a local builder about it and he said it had to do with the negative pressure created with the heat pumps whereas the crawlspace should be addressed with the vapor barrier sealed to the structure ( and I assumed the vents sealed as well). Any help here?
Thanks for the help. Any links to restoration and cost effective energy conservation measures would be appreciated.
Wayne Spinks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
As you suspect, spraying foam under the roof can be problematic unless an eave-to-ridge venting space is left under the decking (you would also need a ridge vent). This can be done with the appropriate vent baffles (such as Accuvent cathedral ceiling vent).
However, insulating the attic floor with additional cellulose would be less costly, as long as you air seal the ceiling thoroughly and seal and insulate the attic ductwork.
The crawlspace should not only have a ground vapor barrier sealed to the perimeter wall, but be insulated, air-sealed and (ideally) conditioned. The floor doesn't need insulation, but the walls do, and spray foam is ideal for this (it can seal the ground vapor barrier at the edges as well). Alternatively, you could install the ground vapor barrier, leave the vents open and insulate under the floor joists with 2" foil-faced polyisocyanurate foam board (assuming there are not a lot of wires or pipes in the way).
It seems like attic temperature is going to be the biggest issue. Can you get any mileage out of some sort of reflective roof coating? Such a thing is virtually non-existent where I build but I assume you have significant cooling needs and with the equipment and ducts in the attic, you're going to want to keep the temperature down. Duct insulation only does so much when the delta T is high.
Wayne,
If you have HVAC equipment and ductwork in the attic, the first choice should always be to insulate the roof and create a conditioned, unventilated attic.
This can be done with closed-cell spray polyurethane foam from the interior (with or without ventilation channels between the foam and the roof sheathing) or with rigid foam board on top of the roof sheathing (in which case you'll need a new roof).
Thanks for the quick responses. The trick is trying to keep the roof undisturbed. The old cement tiles, while they last almost forever, are subject to breaking if you walk on them. Being a historic district, the architectural review board frowns on significant color changes so the reflective coating on the roof probably wouldn't fly unless it wasn't visible from the street.
What about a solar powered roof vent? I know from a maintenance and energy use perspective the hardwired units are frowned upon. Do they move enough air to be useful? I only have one gable end which prominently faces the street so it would have to go somewhere else towards the roof peak I guess.
Is there any way to better insulate the air handler of the heat pump? We talk about duct work but seems like there's hardly any insulating value to what's inside the unit when you take the access cover off.
Thanks for the help.
Wayne Spinks,
Solar-powered roof vents are a waste of money. Read more here:
Are Solar-Powered Attic Ventilators Green?