The upstairs is hot in summer, cold in winter, and the bill says the insulation is not doing its job. Before you buy anything, check what is in the attic now, because the answer decides what to add. This guide uses the US Department of Energy’s insulation fact sheet (2008, so check current numbers) and the insulation videos on this site.
Check this first: what do you have?
- Look in the attic. The DOE sheet says the attic is the easiest place to start. Measure the depth of what you see, and compare it to what the sheet’s table calls the R-value for that material.
- Look in the walls. The sheet says insulation is hard to add to existing walls unless you are adding siding or finishing a space. To check, turn off the power to an outlet on an exterior wall, remove the cover, and shine a flashlight around the box. Check outlets on each floor and in old and new parts of the house, since wall insulation in one place does not prove it is everywhere.
- Look under floors over a garage, basement or crawlspace. For a fibreglass batt, multiply the thickness in inches by 3.2 for the R-value; for foam board multiply by 5, or use the label.
- Look at pipes and ducts in unheated spaces. The sheet says to insulate ducts there, wrap with R-6 duct insulation, and seal leaks with mastic rather than gray cloth tape, which it says degrades.
What an R-value is
R-value is resistance to heat flow, and the higher the number, the better the insulation. It depends on the material, its thickness and density, and R-values of layers add. The sheet adds three cautions:
- Compressed insulation does not give its full R-value. For example, an R-19 batt rated for 6 1/4 in. squeezed into a 5 1/2 in. cavity.
- Thermal bridging. Heat still flows through joists and studs, so attic insulation should cover the tops of the joists.
- Compare products at equal R-values, and read the label: the sheet says US Federal Trade Commission rules require an R-value label on all residential insulation.
How much do you need?
The DOE sheet gives recommendations by climate zone on a map and says they balance future energy savings against the cost of installing insulation, so they vary by zone, energy costs and equipment. It points to a ZIP-code calculator and a table for your area. We have not reproduced the numbers because the map is dated 2008.
The sensible sources for your number:
- The current ENERGY STAR or US Department of Energy recommendations for your climate zone.
- Your local building code, which can differ from those cost-effective levels. In Canada, ask your provincial or municipal building office or your utility’s efficiency program.
- A home energy audit; the sheet says your utility can tell you about one.
One more data point, from the rim joist video: in a 1974 house a single batt filled the rim joist space at R12 then, R14 today at the same thickness, and the presenter says today’s minimum is R20, because homes are framed with 2x6s and code requires the same insulation value downstairs as upstairs. That is his statement for his area. For the shed ceiling, 2 in. of rigid foam board gives R-10 in the video.
Step 1: Seal the air leaks first
The sheet is blunt: air leaks carry moisture and energy, and the attic is often the best place to stop them. Seal them before you add insulation, because the insulation may hide the leaks. Look at:
- cracks where walls meet the ceiling, and around interior door frames
- gaps around electrical boxes, switches and recessed fixtures
- soffits over kitchens and baths
- attic hatches and pull-down stairs
- behind tubs and showers, and around plumbing and wiring penetrations
Step 2: Protect the vents
If the attic is ventilated, the sheet says never cover or block attic vents with insulation, and to use baffles or rafter vents to keep loose-fill from clogging them. Many codes and standards, it says, require one square foot of unobstructed ventilation opening for each 300 square feet of attic floor if the ceiling has a vapor retarder, and twice as much is recommended without one. Check your local code, since this is the sheet’s summary. The openings should be spread equally between soffit and ridge vents or both gables.
Recessed lights: loose-fill must be kept from heat-producing fixtures with baffles or retainers.
Kitchen and bath fans should vent directly outside, not into the attic, where the moisture can cause problems.
Step 3: Add insulation
Safety. Walk only on the joists, since you can fall through the drywall ceiling, and lay boards across them. Wear a dust mask and eye protection, and follow the insulation maker’s safety directions on the package. If you see wires, do not bury or cover junction boxes without checking your local code. Reflective foil conducts electricity, so keep it away from bare wiring.
- Batts or rolls. Use unfaced batts if you’re adding over existing insulation. Lay new batts perpendicular to the old ones to cover the joist tops. Fit the first layer between joists in an uninsulated attic.
- Loose-fill. The sheet says it’s best to hire a contractor for blown-in. Covering the access door matters: an uninsulated hatch reduces savings substantially.
- Stacking. New insulation compresses the old a little. The sheet says to add about one extra inch if the old is fibreglass, or about half an inch if rock wool or cellulose.
- Radiant barriers go near the roof, not on top of insulation, where dust would stop them working.
- Cathedralized attic (insulating the underside of the roof) needs all vents sealed and is best done by an experienced contractor.
Moisture
The sheet notes that adding insulation can cause or cure a moisture problem, because it changes the temperature inside the wall or attic. The shed video repeats it: the number one mistake it names is filling rafter bays without thinking through ventilation, which can lead to condensation, moisture and mould, especially with fibreglass. Its fix keeps the bays open between vented soffits and puts rigid foam under the rafters, at about $350 to $400 USD for a 12×16 ceiling.
Mistakes to avoid
- Insulating over leaks, or over a wet roof deck.
- Stuffing batts into a cavity that is too thin.
- Blocking soffit vents.
- Leaving the attic hatch uninsulated.
- Compressing insulation to fit behind pipes. The sheet suggests splitting the batt so one flap sits behind and one in front of the pipe or wire.
When to call a pro
- Blown-in insulation, spray foam or a cathedralized attic.
- Damaged, burnt or very old wiring in the attic. Do not cover it; call a licensed electrician. See When to Call a Licensed Electrician, Plumber or Gas Fitter.
- Old insulation of unknown type in a pre-1990 house. Health Canada notes asbestos may be found in older building materials; have it tested before disturbing it.
- Mould, roof leaks or a wet deck.
If that didn’t fix it
If the house is still drafty after sealing and insulating, the leak paths are probably in the walls or around windows. See Drafty basement for one example, and book an energy audit through your utility.
Related
- Insulate a rim joist, Insulate a shed ceiling and the Insulation system
- Finishing a Basement: Moisture First, Then Insulation and Framing and Winter Home Maintenance Checklist
- The Basement, Attic and Whole house rooms
Sources
- Health Canada. Asbestos and your health Source
- US Department of Energy, hosted by ENERGY STAR. The R-value table in it is a map image for 2008 and is not quoted here. Insulation Fact Sheet (DOE/CE-0180, 2008) Source
- Shown on this site, source of the rim joist methods and the code remark. Rim Joist Insulation: Batts, Foam Board or Two-Part Spray Foam (video, Home RenoVision DIY) Source
- Shown on this site, source of the R-10 foam board example and the ventilation warning. Insulating a Shed Ceiling With Rigid Foam and Vented Rafter Bays (video, Everyday Home Repairs) Source
Watch
The videos and projects this guide mentions.