Batt in­su­la­tion can lead to mould grief

Winnipeg Free Press - Section G - - HOMES - DAVID SQUARE

AN unin­su­lated base­ment can ac­count for up to 30 per cent of the to­tal en­ergy loss of a house. This chill­ing statis­tic has mo­ti­vated many home­own­ers to re­duce their monthly elec­tric or gas heat­ing bills by in­su­lat­ing their base­ments with fi­bre­glass or stone-wool batts. Here’s the rub: Though this is the cheap­est method of in­su­lat­ing, both types of batts can cause more prob­lems than they solve, in­clud­ing mould growth with se­ri­ous health con­se­quences. To save on con­struc­tion costs, most new base­ments are not in­su­lated on the ex­te­rior side with be­low-grade foam board or other ap­proved ma­te­ri­als. If your base­ment lacks proper ex­te­rior in­su­la­tion (and it likely does un­less built to R-2000 stan­dards), mois­ture and cold will mi­grate from the ex­te­rior to the in­te­rior side of your base­ment. In this case, fi­bre­glass batts are a poor choice of in­su­la­tion be­cause they ab­sorb mois­ture formed by cold and warm air con­dens­ing on the in­te­rior side of a con­crete wall, greatly re­duc­ing the in­su­la­tion’s stated R-value. More­over, fresh con­crete has a high wa­ter con­tent, which takes a long time to dis­si­pate, caus­ing ice to form dur­ing win­ter months on in­te­rior base­ment walls be­hind the in­su­la­tion. In spring when the ice melts, wa­ter will in­fil­trate the batts or, if the con­crete walls have been partly cov­ered by a six-mil vapour bar­rier as rec­om­mended in the build­ing code, run be­hind the vapour bar­rier and pud­dle on or un­der the floor. Trapped mois­ture cre­ates a petri-dish-like en­vi­ron­ment that pro­motes the rapid growth of mould; some types of this fun­gus can col­o­nize (move to an­other area) in less than a week. I no­ticed re­cently Man­i­toba Hy­dro re­placed a video on how to in­su­late your base­ment us­ing fi­bre­glass with an up­dated ver­sion us­ing Roxul in­stead. Roxul is a stone-wool prod­uct spun into batts that re­pel wa­ter and dry more quickly than fi­bre­glass. The the­ory is mois­ture trapped in­side the in­su­la­tion or be­tween the in­su­la­tion and base­ment wall will dis­si­pate be­fore mould spores begin to grow. This is wish­ful think­ing, as some spores are ca­pa­ble of ger­mi­nat­ing in 24 to 48 hours, while mois­ture in­side in­su­lated walls can take months to com­pletely dry. This leaves plenty of time for mould to be­come well-es­tab­lished. In fact, most base­ments in­su­lated with some form of batt will con­tain mould. An ini­tial clue to the pres­ence of mould is a musty smell; how­ever, un­til the prob­lem gets com­pletely out of con­trol and the mould mi­grates to the out­side of a fin­ished base­ment wall, the only way to con­firm the pres­ence of the fun­gus is to re­move a sheet of dry­wall and ex­am­ine the in­su­la­tion. The generic term “black mould” is com­monly used to de­scribe sev­eral types of fun­gus that grow in base­ments. If you have a se­ri­ous mould prob­lem, the in­su­la­tion, wall studs and plates will be cov­ered in black fun­gus that looks like soot. In less ad­vanced sit­u­a­tions, the batts will con­tain mar­ble-like streaks of black, also vis­i­ble on struc­tural mem­bers of the wall. Mould lives on wood fi­bre and cel­lu­lose in pa­per that cov­ers dry­wall. The only way to rid a base­ment of this un­sightly and po­ten­tially toxic fun­gus is to tear out all the in­fested walls, in­crease fil­tered air flow and wash the walls, floors and ceil­ings with one cup house­hold bleach to a gal­lon of wa­ter. (There are other pre­mixed chem­i­cals avail­able from big-box stores, or you can hire a con­trac­tor to do the job for you.) Know­ing th­ese dis­turb­ing facts, it’s cu­ri­ous Man­i­toba Hy­dro con­tin­ues to rec­om­mend the use of batt in­su­la­tion in base­ments through its Power Smart ini­tia­tive. Even more dis­turb­ing is the 2010 Na­tional Build­ing Code of Canada, a source of Hy­dro’s res­i­den­tial con­struc­tion sug­ges­tions, still al­lows batt in­su­la­tion to be used in base­ments, even though North Amer­ica’s best build­ing sci­en­tists have been stat­ing for years that batt in­su­la­tion should never be used in base­ments. (Hy­dro spokesman Peter Kidd said the cor­po­ra­tion could be “show­ing peo­ple a va­ri­ety of ma­te­ri­als” with which to in­su­late base­ments “but batt in­su­la­tion has been around for a long time and proved ef­fec­tive in most cases.”) Ef­fec­tive al­ter­na­tives to batts in­clude spray foam, solid sheets of ex­panded poly­styrene (xps) and poly­iso­cya­nu­rate (poly­iso), as well as a new Hy­dro-ap­proved prod­uct that in­cor­po­rates poly­mer studs and sheets to cre­ate an in­te­grated base­ment-in­su­la­tion sys­tem. Polyurethane spray foam is an ex­cel­lent prod­uct for in­su­lat­ing base­ment walls be­cause it ex­pands and seals the small­est de­cliv­i­ties and cracks in con­crete and acts as a vapour bar­rier at the same time. It has a high in­su­la­tion value of about R-7 per inch. The cons are spray foam is the most ex­pen­sive in­su­la­tion on the mar­ket, and, if not ap­plied in the cor­rect chem­i­cal ra­tio, it will not set prop­erly, cre­at­ing a fishy smell and a po­ten­tial health prob­lem due to con­tin­u­ous off-gassing. Xps and poly­iso are poly­mer-based boards (gen­er­ally sold in four-by-eight­foot pan­els) with in­su­la­tion val­ues of about R-4.5 and R-6.5 per inch, re­spec­tively. They will not ab­sorb mois­ture and can be used to in­su­late in­te­rior base­ment walls by glu­ing them di­rectly to the con­crete with con­struc­tion ad­he­sive for­mu­lated for poly­mers; then seal­ing the joints with tape or canned spray foam. The down­side to this tech­nique is there is no wood frame on which to screw a fin­ish cov­er­ing such as dry­wall. Some peo­ple glue dry­wall di­rectly to the in­su­la­tion board, but this tech­nique is not rec­om­mended, as it does not prop­erly se­cure the dry­wall to the sub­strate. The al­ter­na­tive is to build a wood-frame wall and cut the in­su­la­tion to fric­tion-fit be­tween the studs and plates, seal­ing the join be­tween the wood and in­su­la­tion with bot­tled spray foam. This method is more ex­pen­sive and labour-in­ten­sive, but it will en­sure a solid struc­ture to which Gyproc or other ma­te­ri­als can be screwed or nailed. The cons to poly­mer-based boards are the high cost com­pared to fi­bre­glass or Roxul and, as men­tioned, the need to build a frame wall to prop­erly sup­port the ex­te­rior fin­ish. A less ex­pen­sive al­ter­na­tive is to con­struct a hy­brid wall con­sist­ing of one-inch sheets of xps or poly­iso glued to the con­crete and a wood frame filled with fi­bre­glass or min­eral-wool batts placed over top. This method is also com­pat­i­ble with com­mer­cially ap­plied spray foam. A new prod­uct re­cently ap­proved for Hy­dro Power Smart pro­grams is the Quick-Therm Base­ment and Con­crete In­su­la­tion Sys­tem. It is called a sys­tem be­cause it is com­prised of in­di­vid­ual parts that fit to­gether to form an in­te­grated en­ve­lope that seals air leaks and pre­vents mois­ture in­fil­tra­tion in base­ment walls. More­over, it is sim­ple for a DIYer to in­stall with a min­i­mal se­lec­tion of tools. The main com­po­nents are poly­styrene pan­els cov­ered both sides with a shiny ma­te­rial that re­flects ra­di­ant heat back into the base­ment or re­flects cold air back into the con­crete wall. High-den­sity poly­mer studs are at­tached to the pan­els by a tongue-and-groove joint that is sealed with win­dow and door spray foam. A poly­mer gas­ket seals the pan­els and studs to the base­ment floor. There is no ther­mal bridg­ing (heat trans­fer) be­tween the poly­mer studs or the pan­els, which are held tight to the wall with two plas­tic con­crete fas­ten­ers. The con to this sys­tem is higher cost com­pared to batts. How­ever, at about $3 per square foot, it is less ex­pen­sive than spray foam at $5 to $6 per square foot, but not much more ex­pen­sive to in­stall than a framed base­ment wall con­tain­ing two lay­ers of R-14 Roxul. And that wall could cost you a for­tune to re­move and re­place if mould spores ger­mi­nate in­side of it.

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