Cottage Insulation Retrofit

How to choose the right insulation system to take the chill off your old cottage.

By Craig Saunders

Julia Stratta and Jeff Armstrong bought a cabin on Big Mink Lake, north of Bancroft, about two years ago and immediately started ripping out the insulation. That may seem an odd thing to do when so many cottagers are converting their summer haunts for year-round use. But this particular cabin was so infested by mice that the walls had to be opened up and the old fibreglass insulation removed.

“We didn’t find any live mice,” Armstrong says. But they found lots of “evidence,” and the acrid stench of mouse urine was almost unbearable. They washed the foot-wide plank walls with bleach and water to remove the odour. It was “a nasty, smelly job,” but at the end of the day, the couple had a cabin to call their own. They’d also taken a shine to the rustic look of the exposed planks.

Armstrong and Stratta were left with a dilemma, though: How should they re-insulate their cottage?

Insulating an old cottage so that it will be a cozy retreat, even in the depths of a Canadian winter, is no easy task. A wide variety of materials exists, each with its own drawbacks and advantages, and not all can be installed by a do-it-yourselfer.

Because the couple’s mouse problem forced them to rip open their walls, they have plenty of insulation options. Insulating can be done without ripping the cottage apart, but it’s more difficult, with fewer choices of materials.

Batt Insulation

Anywhere exposed framing can be found, batts are the easiest, cheapest, and most DIY-friendly way to insulate a cottage. Fibreglass is the most common batt material, although there are alternatives such as mineral wool that perform comparably.

Installed properly in a 2 x 6 stud wall, R20 fibreglass batts cost about 55 cents per sq. ft. (R value is a measure of resistance to heat transfer; the higher the number, the better.) More common in older cottages are 2 x 4 stud walls, which take an R12 batt at about 32 cents per sq. ft. The Ontario Building Code has no insulation requirements for cottages, which are defined as seasonal-use buildings. (For houses, it depends on where they are and how they’re heated.) In most situations, cottages in southern Ontario (south of North Bay) will be okay with R20 insulation in walls, and R32 in attics, but Ernie VanKoughnett, deputy chief building official for Seguin Township, suggests beefing up the attic to R40. “The more you put in, the more money you will save in heating,” he says.

For islanders, batt insulation is a good choice, as the bags fit easily in a boat. When buying batts, try to get them in bundles, which are more compressed than individual bags (but at about 40 kg, a six-bundle multipack of R20 is also fairly heavy, so get help loading and unloading the boat).

While cost and ease of installation are two big benefits of batts, there are a few disadvantages, not least the unpleasantness of wriggling around crawlspaces or attics, clutching itchy batts to your chest. Also, as Armstrong and Stratta discovered, mice live quite happily in fibreglass batts. Wind and moisture also penetrate batts easily, so a vapour barrier is essential, ideally combined with an air barrier on the outside.

As warm, moist air meets a cool surface, the water vapour condenses. When this happens inside a wall, it can lead to rotting timbers and mould. To avoid this, a vapour barrier must be installed on the warm side of the insulation. Ideally, it should be hung inside while the interior walls are off. If you’ve removed the exterior siding and decided to insulate at the same time, put the vapour barrier in first from that side, tucking it around the studs.

Another option is to put a vapour barrier over the existing walls inside the cottage. Then just put a new layer of drywall or wood panelling over top of it.

In a pinch, a third method is to seal any cracks and use a vapour-retardant paint on the interior walls.

Rigid Foam Insulation

For cottagers like Stratta and Armstrong, who like the look of exposed plank walls inside their cottage, the insulation has to go on the exterior of the cottage, before adding a new layer of exterior cladding. For this situation, rigid foam is the best bet. It’s easily laid over existing studs or planks, then covered by siding. And if sealed properly, it creates an effective air barrier. “If the air can’t blow in from the outside, then you’ve eliminated most of the problem,” says VanKoughnett. “Rigid foam just doesn’t have the problems that batts do.” Moisture can’t easily penetrate boards made of polystyrene, polyurethane, or polyisocyanurate, three common materials, and mould won’t grow inside them. Because it blocks moisture as well as airflow, a thick layer of rigid foam is a particularly good choice for insulating basements.

Sheathing the outside of a cottage with 1 1⁄2" of rigid foam will provide roughly R7.5 insulation and make it snug for three seasons. More foam will increase the R value, but those additional inches may mean that exterior flashings need to be extended before re-siding the cottage.

All foam insulation must be covered, preferably by a fireproofing material such as drywall on the inside, because when foam burns, it emits a very toxic smoke. Keep in mind, too, that your materials costs for rigid foam will be at least three times as much as for fibreglass batts.

Loose-Fill Insulation

Cellulose, fibreglass, and mineral wool insulation can be purchased in bales, then fed into large machines that chop up the material and, with powerful fans, blow it through a hose into a wall or attic.

While loose-fill fibreglass, known as “blown-in blanket system” or BIBS, must be installed by a contractor, mineral wool and cellulose blowers can be rented at many cottage-country building supply stores (check for availability in advance). If you want to do it yourself, head for the attic, where blown-in material is easy to install and a good alternative to crawling around with batts. But make sure you have help. It takes two people: one inside the cottage, the other feeding the machine.

The biggest advantage of loose-fill insulation is that it can be blown through 1"–2" diameter holes, so walls needn’t be torn down. This process is commonly referred to as “drill and blow,” or “drill and fill.” But getting the right density in the walls is tricky, so professional installation is a good idea.

Since the pros use massive blowers mounted on huge trucks, blowing in loose fill takes a fraction of the time installing batts or rigid foam would take. That makes BIBS very competitive with professionally installed batts, explains Huntsville contractor Dan Johnson. If the studs are exposed, BIBS costs about $1.25 per sq. ft. in 2 x 6 walls and about $1 in 2 x 4 walls. The result is a snug fit with no gaps to carry air and moisture to the cold exterior wall. Drill-and-fill jobs are more labour-intensive, and cost about $2.50 per sq. ft.

One surprise is how tidy a professional job is. When BIBS is installed in an exposed stud wall, the studs are covered with a membrane that allows air from the blower hose to escape, while trapping the fibreglass so there’s no insulation flying about. Also, with no cutting of batts, there’s little waste to dispose of.

There are drawbacks. If you’re insulating an island cottage, look for another material because the blowers are big enough that they are usually loaded into a pickup truck using a forklift. Don’t even think of putting one in your bowrider, unless you plan on insulating the lake bottom. One type of loose-fill, cellulose, has its own concerns: flammability and infestation by mice. If you choose it, be sure it has fireproofing and anti-vermin additives.

After his experience with fibreglass batts and rodents, Armstrong remains sceptical that loose-fill materials will solve his mice problem. While mineral wool is denser than fibreglass and that should discourage nesting, he says, “it’s not necessarily proof.”

Polyurethane Foam

The material VanKoughnett praises above all others is polyurethane foam. Sprayed into place, it expands into an airtight system of tiny bubbles that will fill any cavity tightly. Polyurethane is not the same as urea-formaldehyde foam insulation (UFFI), which was banned in 1980 because improper installation could result in the off-gassing of formaldehyde.

“The urethanes of today form a skin,” says VanKoughnett, who adds that polyurethane foam must be installed by licensed contractors.

It goes in easily, creates an airtight seal that blocks moisture and, at roughly R6.5 per inch, outperforms all competitors on R values, making it an excellent choice for cathedral ceilings or the floors of cottages on piers. For cottagers like Stratta and Armstrong, VanKoughnett gives one final thumbs-up to polyurethane: “Critters don’t tend to bother it.” But such advantages come at a price: about $3 per sq. ft. to get 3" installed.

After their initial investigation, Armstrong says they haven’t settled on what to do. The couple isn’t convinced that any insulation will keep rodents out for certain – at least, not the options that will maintain the rustic look of their exposed-plank walls. Armstrong, a project director for an architect, had considered creating a temporary installation containing a reflective material. This would bounce heat from the woodstove back into the cottage, and could be taken down in the spring, much like the walls of a yurt.

Then again, they may leave the cottage the way it is, and build an insulated addition to keep them warm on the coldest days of winter. It’s not ideal, but if it were perfect, it just wouldn’t be the cottage, would it?

 

 

Writer and editor Craig Saunders is itching to insulate an imperfect Bruce Peninsula cottage he frequents.

*Published in the October 2005 issue of Cottage Life.

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