Place­ment of in­su­la­tion im­por­tant in crawl space

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

QI have a ques­tion that I have not been able to an­swer through my ex­ten­sive re­search and I ap­pre­ci­ated the light you shed on heated cold crawlspaces. My sit­u­a­tion is that I have a crawlspace be­low my kitchen which has an out­let from my forced air gas fur­nace. When ren­o­vat­ing two years ago, my con­trac­tor sealed the soil floor with heavy poly­eth­yl­ene, pink foam board in­su­la­tion, seams sealed with tuck tape, on walls and floor and then he topped it with Roxul in­su­la­tion. I’m not sure if this is a fire bar­rier per build­ing code or for in­su­la­tion. The is­sue is that I had the con­trac­tors cut two reg­is­ter holes to run cor­ru­gated ducts from the forced air out­let, which re­duced the air­flow re­mark­ably and caused the space to get colder due to lack of air dis­tri­bu­tion. So I de­cided to re­move the ducts in or­der to re­gain the heat back to the crawlspace. I tried to in­stall fil­ters on the reg­is­ters in or­der to al­le­vi­ate the con­cern that Roxul fi­bres would en­ter the living space. This proved too labour in­ten­sive, hav­ing to en­ter the tight crawlspace on a regular ba­sis to re­place the fil­ters. I later de­cided to tuck tape the reg­is­ters shut, but this has again left me in the po­si­tion that the space is un­com­fort­ably cold on our sub -10C days. In your opin­ion, can I re­move the Roxul, clear the air with high speed con­struc­tion fans and re­open the vents with­out a con­cern of go­ing against code? If I will be vi­o­lat­ing code can I lay down fire-rated dry­wall and achieve the same prop­er­ties? My dad sug­gested in­stalling a tarp over­top, in the space that mea­sures 20x15x12”, but that was way too tight and sloppy for my lik­ing. I would ap­pre­ci­ate any in­put you can pro­vide, Matthew Gregg. An­swer: I am glad you have read one or more of the ar­ti­cles I have writ­ten on the most ef­fec­tive way to in­su­late and heat a crawlspace, but you may have missed at least one crit­i­cal item. Not only are your heat­ing mod­i­fi­ca­tions prob­lem­atic, the in­su­la­tion ap­pears to be in the wrong lo­ca­tion. I will try to steer you in the right di­rec­tion, so you can have a dry, safe, and warm crawlspace be­low your kitchen. The first things to ad­dress are not only the type of in­su­la­tion ma­te­ri­als used, but the lo­ca­tion of those ma­te­ri­als. It is a lit­tle bit un­clear from your sub­mis­sion ex­actly where the in­su­la­tion is in­stalled, but it ap­pears the con­trac­tor may have im­prop­erly lo­cated at least some of the it. To un­der­stand this more eas­ily you must re­al­ize there is no ad­van­tage in putting in­su­la­tion on the dirt floor. The poly­eth­yl­ene sheath­ing is im­por­tant as an air/vapour bar­rier in this lo­ca­tion, to pre­vent mois­ture in­tru­sion from the soil into the heated crawlspace, but that is all you need over the dirt floor. If the rigid foam is on the floor, re­move it and it could be re­pur­posed on the in­side of the walls of the crawlspace. In­stalling min­eral fi­bre batt in­su­la­tion on top of the foam will not be a good idea and it is doubt­ful it will be suf­fi­cient for fire pro­tec­tion for the ex­truded poly­styrene (XPF) sheath­ing. It is even un­likely you will need fire pro­tec­tion on top of any foam in­su­la­tion, to meet lo­cal build­ing codes, be­cause the crawlspace is not part of the living space. The only pro­tec­tion that would help would be fire-rated dry­wall and you never want to in­stall dry­wall in a crawlspace, due to the po­ten­tial for mois­ture ab­sorp­tion and mould growth. So, the first step in im­prov­ing your crawlspace warmth is to re­move any in­su­la­tion from the top of the soil. The next area to ad­dress is the use of batt in­su­la­tion in the crawlspace. It should not be in­stalled af­ter the XPF and then cov­ered with poly­eth­yl­ene sheath­ing. That will cre­ate a dou­ble air/vapour around the batts, which may cause mois­ture to be trapped next to the min­eral fi­bre, wet­ting it. This will ren­der it some­what in­ef­fec­tive and cre­ate the po­ten­tial for mould growth on dirt or de­bris in the same area. The best way to ap­proach the in­su­la­tion in your shal­low crawlspace is to in­stall it only on the in­side of the perime­ter walls of the crawlspace. Whether th­ese walls are cre­ated from a con­crete grade beam, or from a wood skirt­ing, that is the only area that needs to be in­su­lated. If I un­der­stand you cor­rectly, there al­ready is a layer of XPF on this area, so adding more lay­ers will im­prove the ther­mal re­sis­tance and keep the crawlspace warmer. You can re­use the use­less foam sheets that were im­prop­erly laid over the poly on the floor of the crawlspace and leave them un­cov­ered, ex­cept for seal­ing any seams or gaps. If I have mis­con­strued your notes, and the foam sheath­ing is in­stalled on the un­der­side of the wood kitchen floor sys­tem, it should also be re­moved and re­lo­cated to the crawlspace perime­ter. That lo­ca­tion for the in­su­la­tion would only help to make the kitchen floor colder, by trap­ping heat in the crawlspace, not al­low­ing warm air to rise into the room above. The last item to ad­dress is the heat­ing sys­tem. For­get about us­ing flex­i­ble duct­ing and do­ing the work your­self. Your ter­mi­nol­ogy of “forced air out­lets” is com­pletely im­proper and con­fus­ing, and I have no idea where or what you have done to heat the kitchen or crawlspace. Af­ter the in­su­la­tion re­pairs are com­pleted call a li­censed HVAC con­trac­tor to in­stall proper ducts and reg­is­ters, both in the crawlspace and the kitchen, and you will have a com­fort­able and safe home. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the past pres­i­dent of the Canadian As­so­ci­a­tion of Home & Prop­erty In­spec­tors. He can be reached at 204-291-5358 or check out his web­site at trained­


The best way to ap­proach the in­su­la­tion in your shal­low crawlspace is to in­stall it

only on the in­side of the perime­ter walls of the crawlspace.

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