Don’t make these three base­ment fin­ish­ing mis­takes

Fin­ish­ing your base­ment is the most eco­nom­i­cal way to add com­fort­able liv­ing space to your home

The Southern Gazette - - Saltwire Homes - Steve Maxwell House Works House Works by Canada’s Handi­est Man’ Steve Maxwell fea­tures DIY tips, how-to videos and tool prod­uct reviews. Feel free to say send him an email to say hello or to ask a tech­ni­cal ques­tion or make a com­ment at steve@steve­maxwel

Win­ter is the sea­son when Cana­di­ans most cher­ish the idea of a fin­ished base­ment. Sure, it’s great to have one any time, but as the winds swirl and snow blows out­side, there’s some­thing es­pe­cially at­trac­tive about snug­gling into a comfy couch or easy chair in your warm, bright, invit­ing sub­ter­ranean space.

The thing is, most home­own­ers and some pro­fes­sional builders don’t re­al­ize how easy it is to fin­ish a base­ment in­cor­rectly. Even if things look great on the sur­face, com­mon de­sign mis­takes can en­cour­age mould, mildew and hid­den cor­rup­tion be­hind the scenes in your base­ment — none of which can be fixed eas­ily af­ter the fact. This is why the best way to fin­ish a base­ment is to do it dif­fer­ently than the way it’s al­ways been done.

The pri­mary chal­lenge when it comes to fin­ish­ing a base­ment is main­tain­ing good in­door air qual­ity through­out your home. Com­fort, suf­fi­cient light and a pleas­ant floor plan are all im­por­tant, but they don’t mat­ter much if your base­ment is pol­lut­ing your in­door air with mould spores. The unique dan­ger with base­ments is that mois­ture in the form of liq­uid wa­ter leaks, mois­ture vapour and con­den­sa­tion will en­ter wall cav­i­ties and floors, trig­ger­ing the growth of mould and mildew on or­ganic ma­te­ri­als. A well fin­ished base­ment is al­ways dry, but also has some ca­pa­bil­ity to han­dle un­ex­pected mois­ture.

Base­ment Fin­ish­ing Mis­take #1: Hav­ing Too Much Hope

Even the wettest base­ments in the world look dry at some times of the year. And even the small­est amount of leaked wa­ter will have dis­as­trous ef­fects if it hap­pens be­hind a wood frame stud wall or into the pile of broad­loom. All this is why it makes sense to hold your base­ment fin­ish­ing en­thu­si­asm in check and give your­self a chance to prove for sure that your base­ment re­ally is dry. It’ll cost tens of thou­sands of dol­lars to fin­ish your base­ment in even the sim­plest way, and this is a sig­nif­i­cant risk if you go ahead with­out mon­i­tor­ing that your base­ment is truly dry over at least one full year be­fore fin­ish­ing.

Base­ment Fin­ish­ing Mis­take #2: In­stalling Car­pet on Con­crete

Even with the ad­di­tion of thick un­der­lay, wall-to-wall car­pet on con­crete base­ment floors is bad for two rea­sons. First, if you have any kind of a leak — no mat­ter how small — it’s go­ing to soak the car­pet and kick­start mould. And sec­ond, car­pet can en­cour­age droplets of con­den­sa­tion to de­velop along the con­crete floor dur­ing warm, hu­mid sum­mer­time weather. Both these prob­lems can be solved with the right kind of sub­floor un­der­neath what­ever fin­ished floor you choose. Ev­ery build­ing sup­ply store sells base­ment sub­floor tiles these days. They cre­ate a slightly el­e­vated space un­der­neath to sep­a­rate fin­ish­ing floor from con­crete and cre­ate a small drainage chan­nel un­der­neath in the event of a small wa­ter leak.

Base­ment Fin­ish­ing Mis­take #3: In­ap­pro­pri­ate

Rim Joist In­su­la­tion

Rim joists are the ar­eas where the floor frame of the first floor of your house meets the out­side walls in the ceil­ing of your base­ment. Al­most ev­ery home I ex­am­ine has mould growth on the fi­bre-based in­su­la­tion be­hind vapour bar­rier plas­tic in­stalled in rim joist ar­eas. As com­mon and code-com­pli­ant an ap­proach as this is, it sim­ply doesn’t work. The code def­i­nitely needs to be up­graded. There’s sim­ply no way you can in­stall plas­tic to seal out the warm, moist in­door air from in­fil­trat­ing the fi­bre in­su­la­tion, cool­ing within it dur­ing win­ter, and form­ing mould-pro­mot­ing liq­uid wa­ter droplets in­side. At least a three-inch depth of closed cell spray foam is the only way to seal and in­su­late rim joist ar­eas prop­erly.

Fin­ish­ing your base­ment is the most eco­nom­i­cal way to add com­fort­able liv­ing space to your home. You’ve al­ready got a roof and ex­te­rior walls, you just need to di­vide up the base­ment and make it nice. Just be sure to do it so mould doesn’t get a chance.

Steve Maxwell hates in­door mold in all its forms. Visit Canada’s largest col­lec­tion of howto and home im­prove­ment ar­ti­cles and videos at Bai­leyLineRoa­


A beau­ti­ful fin­ished base­ment is a great home fea­ture, but en­dur­ing suc­cess de­pends on avoid­ing spe­cific com­mon mis­takes that pro­mote mold and harm­ful in­door air qual­ity.


This base­ment al­lows no or­ganic mat­ter to touch ma­sonry walls or floors. When this strat­egy is ap­plied to a truly dry base­ment, the re­sult is lon­glast­ing fresh­ness and free­dom from mold.

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