Building Homes or Extensions/Insulation


I am remodeling a 1925 western bungalow in Cleveland, Ohio similar to the picture I have attached. I have an unconditioned central attic space that I use for storage with 2x4 roof rafters and soffits and ridge vent for ventilation. I will be gutting my dormer space and bedrooms of the plaster and lath and intend to insulate the sloped ceilings as there is not any currently. I would like to do spray foam insulation to maximize my r-value with the limited space of the existing structure I have to insulate. What is the depth of the air flow channel I need to consider for proper airflow for the roof. Would I use Closed or open cell insulation? Would I stop insulating the rafter space where the bedroom/dormer ceilings end or carry all the way to the peak? Do I need to add a vapor barrier between the insulation and drywall? Thank you for the reply.


I would deepen the rafters by attaching 1-1/2" x 2" buildouts along each one, to give you adequate depth for insulation and ventilation.  See attached sketch.

You can use closed cell foam along the rafters, as long as you provide ventilation as shown, by using foam baffles or similar.  Use faced fiberglass batts on the ceiling joists and wall studs.

Let me know if you have any questions, and best of luck.

--Steve Major

Building Homes or Extensions

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Stephen Major (Owner--Major Design Group)


I can answer any questions regarding the design and construction of homes and additions. This includes trade-specific questions (how-to) in all major building trades: framing, foundations, site prep, electrical, HVAC, plumbing, water treatment, interior finishing, trim & cabinetwork, exterior finishing, roofing, siding. PLEASE indicate your state or region, so I can provide the best possible answer. PLEASE provide photos whenever possible.


30 years experience in building design and construction, all hands-on, including the construction of dozens of single-family homes and hundreds of remodeling projects in the northeastern US.

Author: "Architectural Woodwork - Details for Construction" published by Van Nostrand Reinhold (now Wiley).

BS Cornell University.

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