Dormer vents/attic ductwork
Hello! We are gut renovating our 800 sq ft house to add ~600 sq ft. A new roof for the whole house.
Some notes:
– located in Los Angeles, CA
– dirt floor crawl space
– heat pump outside, with air handler and duct work in the attic
– adding an erv, also in the attic
– heat pump water heater in the center of the house, ducted to the attic
Current plan from the architect/contractor is to have insulation at ceiling level, and gable vents in the addition portion of the house.
I don’t know much about gable vents, and wondering if that is the best solution here.
Should I prioritize insulating the roofline because of the duct work? And not vent the attic?
I’m attaching drawings from our architect – blue hash lines are the addition portion.
Thanks in advance for any insight!
Katie
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Replies
I also have an uninsulated attic, ventilated via louvered openings at the gable ends. I live in Phoenix. Like Los Angeles, those attics get HOT, and it's not ideal to have ductwork or HVAC machinery up there, if you can help it. It's nice to have an attic that is encapsulated in the conditioned space fully insulated and air-sealed, but it's a big project to consider.
The trick here is that you're not just talking about insulation, you're talking about expanding the building envelope, and that will change the technology behind the whole structure. An architect will have to advise you on the wall-to-rafter connections, how to detail your weather and air barriers, what kinds of roof materials to use, etc. etc. You'll also need to add ductwork and supply the attic itself, or risk some potential problems with humidity. This might mean a bigger heat pump too.
An alternative that a lot of folks do here is to replace ordinary roof sheathing with radiant barrier, to block as much infrared radiation as you can, and to add some kind of forced air circulation to keep the attic continually supplied with cooler air. If the living space is well sealed, you shouldn't have too much infiltration from above. Same with ductwork.
Good luck!
Hi Katie,
Scott's advice is good, make the attic space part of the home so that the ducts and any HVAC equipment is also inside, not in a vented attic which is outside. You mentioned a crawlspace, you also need to decide if that space is inside or out. If it is outside, you will need to insulate and air seal the floor between the crawlspace and living space and vent the crawlspace. We are seeing more conditioned crawlspaces which moves the insulation and air sealing to the crawlspace walls, in this case, there is no venting of the space to the outside. You also need to cover the dirt floor with a vapor retarder, polyethylene sheeting, 6 mil minimum. If there is enough room, the HVAC equipment could also be located in the crawl instead of the attic.
Good luck with your project,
Randy
Thank you Scott and Randy for your sound advice! I will take this all to our architect and contractor.
best,
katie
Scott and Randy’s advice is great if the only option for your HVAC system is to locate it in the attic. Understand that the conditioned attic suggested is only marginal better than the current truly awful condition.
Conditioning the attic almost forces you to use spray foam. It is the most expensive way to buy an R of insulation. In fact spray foam is so expensive installing the code required R value doesn’t make economic sense because it can never pay for itself. Also spray foam is the least green insulation on the market and the very real possibility for it to be improperly installed.
Consider finding the space below the ceiling for your system or going ductless.
My guess is your old house is very leaky. So leaky that installing an ERV is almost comical. Put the ERV idea on hold until you can get a blower door test under 2 ACH50. Spend that money on more and better air sealing.
Seems to me in a cooling dominated climate ducting the HPWH to the attic is wasting energy. As every BTU the HPWH removes from the house is one less BTU the AC system must provide.
Walta