Insulating with an old tile roof
Emily here. I posted last week about the insulation design for our 1914 bungalow (which has the original stucco exterior and red barrel tile roof), and got some great advice about how to insulate the kitchen walls, which are currently open. This house is located outside Boston, so climate zone 5A.
I’m posting hoping for some similarly great advice or feedback about our attic/kneewall/roofline insulation plan. I feel like we are over thinking this, but I am also very worried about inadvertently causing a catastrophe, like the roof deck failing. We have a GC, an insulation contractor, and an independent energy consultant/HERS rater who are all pretty much telling us different things. My priority is doing the right thing for the house.
1. The roof has wood sheathing and the aforementioned tiles. In some places along the front there is an ice and water barrier added in 2017, but mostly to my knowledge there is nothing between the wood and the tiles.
2. This being a bungalow which is effectively 1.5 stories, there are knee walls at the front and back of the house with voids behind them. There is one big kneewall void at the back and two at the front (on either side of a shed dormer). The “attic” above the second floor is very small and has historically had no access. The floor of the kneewall void in the back of the house has some old insulation under it which would be very difficult to remove. There is no eave or peak/gable venting currently.
3. The house has been heated with hydronic radiators (oil-fired boiler). We’re keeping that, but adding a ducted mini-split system. The air handler will go in the kneewall void at the back of the house, and the ducting will be in there and run through the attic.
4. After we took out the second floor ceiling (to facilitate insulation and HVAC), it became apparent there has been water coming through the tile roof cladding and soaking the wood sheathing. Not a huge amount of water; the old horsehair plaster ceiling showed no damage at all from inside the living space. But without the plaster, you can see water marks all over the wood sheathing and when it rains, there are drips in some places. We have had roofers out twice to fix it, but it’s not easy to find the problem tiles from the exterior.
The original insulation plan (from the insulation contractor) was to insulate the roofline: install baffles on the underside of the roof sheathing, net and blow cellulose into the rafter bays, cover that with 2″ rigid foam. The water situation made us think that is a bad idea.
The energy consultant suggests putting in baffles and spraying the whole roofline with closed cell foam. Similarly, we worry about water coming in from the exterior of the tiles.
So, there is a new plan, to insulate the living space (the kneewall void floors, the kneewalls, the clipped ceilings, and the attic floor). We are having trouble identifying the right materials for this – likely a combination of rock wool and loose fill, depending on location, with baffles in some places. This is also a much more involved plan and would leave our air handler and ducts in unconditioned space.
We are doing the best we can, but it’s not easy. Can anyone advise? Thank you for any thoughts.
Couple photos attached, of the underside of the roof, the interior of the second floor, and the front of the house showing the dormer.
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