Mois­ture un­der sub­floor causes mould smell

Winnipeg Free Press - Section F - - HOMES - ARI MARANTZ

QI’m hop­ing you can give us some help with our base­ment floor. Our home is in North Kil­do­nan and was built in the mid-’80s. It is a bun­ga­low in ex­cel­lent con­di­tion with an un­fin­ished base­ment.

We have de­cided to par­tially fin­ish the base­ment and my hus­band started lay­ing down Dri-Core floor tiles as a base, prior to in­stalling floor­ing. We had heard that this is the so­lu­tion to pro­vid­ing good air flow un­der­neath, as well as pro­tec­tion from mois­ture and cold on the sur­face.

Since lay­ing down a small area last sum­mer, at the bot­tom of the base­ment stairs, we started notic­ing a musty mildew smell. When my hus­band lifted a sec­tion of the tiles, along with sow bugs and spi­ders there was a dis­tinct mould smell and the pres­ence of white pow­der, ef­fer­ves­cence, around the base of the walls. Be­fore we continue with in­stalling any floor­ing we would like to know if we are do­ing some­thing wrong here.

We have a new fur­nace, a top-of- the-line Len­nox, that was in­stalled 18 months ago. We keep a de­hu­mid­i­fier run­ning all sum­mer long, to­gether with the air con­di­tioner, but no other air mod­i­fi­ca­tion. Any help you can give us would be greatly ap­pre­ci­ated. Thank you in ad­vance. Judi Parry AN­SWER: The an­swer to your ques­tion may be dif­fi­cult to pin­point, but the goal is to stop wa­ter seep­age into your base­ment. While it may not be read­ily ap­par­ent, the cause of the smell is from mould that oc­curs due to mois­ture un­der the sub­floor. To elim­i­nate this, you will have to find out where it is leak­ing and stop the wa­ter in­tru­sion to pre­vent fur­ther oc­cur­rences.

The sub­floor ma­te­rial you have in­stalled in your base­ment is a good prod­uct to keep your floor­ing dry and make the floor warmer, but it has lim­ited abil­i­ties to man­age wa­ter. The slightly el­e­vated plas­tic sur­face on the un­der­side of this ma­te­rial will pro­vide a small air space to al­low some air move­ment, but may not be ad­e­quate if a mod­er­ate to large amount of mois­ture leak­age oc­curs.

If small amounts of mois­ture get un­der­neath, due to con­den­sa­tion or mi­nor seep­age, the airspace may pro­vide enough air­flow to help this mois­ture evap­o­rate. If more fre­quent or larger wet­ting oc­curs, this wa­ter may not be able to fully es­cape this small cav- ity. When that oc­curs, dirt and dust or other de­bris un­der the sub­floor could be­come a sub­strate for mould growth.

The ef­flo­res­cence you are see­ing when you lift the in­di­vid­ual sub­floor tiles is caused by min­er­als leach­ing from the con­crete. This oc­curs from wa­ter that ei­ther leaks un­der the sub­floor, or from mois­ture within the con­crete slab, it­self. These salty crys­tals them­selves are harm­less, but they are a sign of po­ten­tially larger is­sues.

The musty smell you notice is likely caused by mould growth, which may be form­ing on de­bris un­der this area or in the OSB sheath­ing of the sub­floor it­self. While the plas­tic sheath­ing on the un­der­side may help pre­vent this, it will not elim­i­nate the pos­si­bil­ity if wa­ter sits un­der the sub­floor pan­els for an ex­tended time. Adding more ven­ti­la­tion may be the first step to fix­ing this is­sue.

Most man­u­fac­tur­ers of this style of sub­floor­ing ma­te­rial re­quires ad­di­tional vents to be cut in the sur­face of the sub­floor at var­i­ous in­ter­vals. This may be re­quired mainly around the perime­ter of the com­pleted sub­floor, or along par­ti­tion walls. These open­ings can be cov­ered with typ­i­cal heat­ing reg­is­ters or other vented cov­ers, but they are es­sen­tial to al­low proper air­flow be­low the sub­floor­ing.

I would rec­om­mend cut­ting sev­eral of these vent holes, as per the man­u­fac­turer’s spec­i­fi­ca­tions, to im­prove air­flow un­der this sur­face. While this may help pre­vent prob­lems in the fu­ture, look­ing out­side the foun­da­tion is the next step.

Many seep­age in­ci­dents into base­ments are cause by a com­bi­na­tion of poor ex­te­rior grad­ing and drainage. If the soil has eroded and ap­pears de­pressed out­side the foun­da­tion in the area where you’re see­ing your prob­lem, some land­scap­ing is re­quired. Build­ing up the soil in this area to pro­vide a small slope away from the foun­da­tion is the an­swer. Plant­ing grass seed, sod or low veg­e­ta­tion af­ter the soil in­stal­la­tion may also help pre­vent fur­ther ero­sion.

Since this is hap­pen­ing near the base­ment stairs, there is a chance that there may be a large hid­den void un­der­neath a land­ing or stair­way out­side this area. If you have a back or side door at the top of these stairs, that may be the case. Again, the so­lu­tion to the is­sue should be to dig un­der this area and fill the void to pre­vent fur­ther seep­age.

Check­ing to see that eave­stroughs are in good con­di­tion and clean is the next task. Also, if down­spouts are dump­ing near the foun­da­tion, ex­ten­sions should im­me­di­ately be in­stalled to di­vert the wa­ter one to three me­tres away from your house. The ma­jor­ity of mois­ture in­tru­sion I see in base­ments oc­curs near cor­ners or other ar­eas where the down­spouts are ter­mi­nat­ing.

The plas­tic-coated, tongue-and­groove sub­floor­ing ma­te­rial you have cho­sen is a good prod­uct for keep­ing floor­ing off con­crete base­ment floor slabs, which has sev­eral ben­e­fits, but may not be ef­fec­tive if the floor is con­sis­tently wet. It will cre­ate a ther­mal break be­tween the floor­ing and the cool con­crete, pre­vent­ing wick­ing of mois­ture into the floor­ing, and will also make the sur­face warmer. In­stalling ad­di­tional vents, par­tic­u­larly around the perime­ter of the floor, and ex­te­rior wa­ter man­age­ment is still nec­es­sary to help pre­vent sig­nif­i­cant seep­age that can al­low mould and dam­age to oc­cur to the sub­floor.

If the sub­floor­ing con­tin­ues to smell, or be­come mouldy, af­ter ad­dress­ing these is­sues, a more costly foun­da­tion wa­ter­proof­ing re­pair may be re­quired. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the pres­i­dent of the Cana­dian As­so­ci­a­tion of Home & Prop­erty In­spec­tors - Man­i­toba (www. Ques­tions can be e-mailed to the ad­dress be­low. Ari can be reached at (204) 291-5358 or check out his web

site at www.trained­

The con­crete pad poured in place of a base­ment has eas­ily sup­port­red Greg and

Elane Sin­clair’s home north of Tyn­dall for decades.

Large cracks in an above-grade base­ment wall were caused by sink­ing and shift­ing.

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