Be­tween a wall and a cold space

The Glengarry News - Glengarry Supplement - - News -

Walls can ac­count for about 20 per cent of heat loss in houses. In ad­di­tion to heat loss through the walls, there are many cracks and pen­e­tra­tions that al­low un­con­trolled air leak­age into and out of the house.

Solid walls – built of brick, stone, con­crete block, log or wood plank – do not have a cav­ity that can be in­su­lated. The only op­tion is to add in­su­la­tion to the ex­te­rior or to the in­te­rior. Many solid walls, in­clud­ing dou­ble brick walls have a small cav­ity, gen­er­ally less than 25 mm (1 in.), which is a drainage plane that col­lects and drains wa­ter out of the wall. Never in­su­late these cav­i­ties or plug their drain holes.

Con­crete-block walls usu­ally have hol­low cores that al­low air cir­cu­la­tion within, in­creas­ing con­vec­tive heat losses. In­su­lat­ing the cores of­fers min­i­mal ther­mal re­sis­tance since the blocks’ in­ter­nal webs and mor­tar will con­tinue to act as ther­mal bridges. In­stead, seal all pos­si­ble air leak­age routes into the block wall and en­sure that the top course of blocks is capped. Where block walls form the party walls be­tween hous­ing units, air leak­age of­ten oc­curs in the space be­tween the block wall and the in­te­rior fin­ish. Make sure the space is fully air sealed.

Frame walls have a cav­ity that may be in­su­lated. Dif­fer­ent con­struc­tion tech­niques de­ter­mine the size of the cav­ity and ease of ac­cess from ei­ther the in­te­rior or ex­te­rior. The wall con­struc­tion also af­fects de­tails that can in­ter­fere with the in­su­la­tion, in­clud­ing top and bot­tom plates, fire stops, block­ing, plumb­ing, wiring and heat­ing ducts. A frame house with a brick ve­neer usu­ally has a 25 to 50 mm (1 to 2 in.) air space be­tween the bricks and the frame wall as part of the drainage plane. Do not in­su­late this space. Fur­ther­more, in­su­lat­ing over the sur­face of an ex­te­rior wall that in­cludes a drainage plane air space will sim­ply not be very ef­fec­tive. It is bet­ter to add the in­su­la­tion di­rectly to the ex­te­rior of the frame wall and then in­cor­po­rate the ap­pro­pri­ate air bar­rier, drainage plane and sid­ing, un­less the spe­cific prod­uct and its in­stal­la­tion di­rec­tions ac­count for these re­quire­ments. The larger cav­ity in the frame wall can be in­su­lated.

Op­por­tu­ni­ties for up­grad­ing

Us­ing dense-pack in­su­la­tion tech­niques, empty cav­ity and some par­tially in­su­lated cav­ity frame walls can be in­su­lated from the top and bot­tom or from the in­te­rior or ex­te­rior.

Walls can be in­su­lated as part

of a ma­jor re­pair job or ren­o­va­tion. In­te­rior work in­cludes wall re­pairs, elec­tri­cal wiring up­grades, in­su­la­tion and vapour bar­rier in­stal­la­tion, dry­wall and fin­ish­ing. On the ex­te­rior, in­su­lat­ing can be com­bined with re­sid­ing.

Ad­dress any mois­ture or struc­tural prob­lems be­fore in­su­lat­ing. In­di­ca­tions of prob­lems in­clude stain­ing, mould growth, rot, cracks on the in­side and ex­te­rior wall fin­ishes, and win­dows and doors that do not op­er­ate prop­erly be­cause they are out of square. It is im­por­tant to con­sider both vapour bar­ri­ers and air bar­ri­ers, es­pe­cially when ad­ding in­su­la­tion to the in­te­rior or ex­te­rior of an ex­ist­ing wall.

The vapour bar­rier must be on the warm third of the fin­ished wall.

Also con­sider the lo­ca­tion and con­di­tion of old vapour bar­ri­ers, which could be as sim­ple as plas­ter walls with sev­eral coats of paint.

To­day, pro­fes­sional in­su­la­tion con­trac­tors can blow in loose-fill in­su­la­tion or in­ject ap­proved foam in­su­la­tion into even par­tially in­su­lated wood-frame wall cav­i­ties. Us­ing dense-pack tech- niques, cel­lu­lose, glass fi­bre and ap­proved foams will com­press ex­ist­ing batt in­su­la­tion and fill all the re­main­ing voids while also of­fer­ing good air seal­ing val­ues. Since the stud space is likely only about 89 to 102 mm (3 to 4 in.) thick, ther­mal re­sis­tance gains may be lim­ited, es­pe­cially if the wall al­ready con­tains some in­su­la­tion. How­ever, next to ad­ding ei­ther in­te­rior or ex­te­rior in­su­la­tion, good re­sults can be had. Be­fore pro­ceed­ing, try look­ing be­hind elec­tri­cal out­lets – with the power off – to find out what al­ready ex­ists in the walls.

To in­su­late, small holes must be drilled into each stud space. In most cases, one to five holes must be drilled per storey, in­clud­ing those above and blow win­dows and doors. A long tube is in­serted through each hole into the cav­ity from the top or the bot­tom of the stud space. The hose is then with­drawn in stages to al­low the space to be filled to the proper den­sity.

Choose your in­su­la­tion prod­uct and in­stal­la­tion method care­fully. Con­sult closely with a con­trac­tor with a proven track record to ob­tain the best re­sults. Stip­u­late the man­u­fac­turer’s rec­om­mended den­si­ties for the ma­te­rial in the con­tract with the in­staller. The con­trac­tor will need to ver­ify the amount and den­sity of the ap­pli­ca­tion and then you and the con­trac­tor should agree on the num­ber of bags or con­tain­ers to be used.

Only a small vari­a­tion from this tar­get is ac­cept­able as too lit­tle will leave voids and/or set­tling gaps in the walls. If too much is used, some of the in­su­la­tion may be es­cap­ing from the wall into the floor space or some other area where it is not needed. Too high a den­sity can cause walls to bulge. Also ver­ify with the con­trac­tor ex­actly how the holes will be sealed, patched and fin­ished.

In­stalling the in­su­la­tion

There are three ways to in­stall the in­su­la­tion: from the in­side, from the out­side, from the base­ment/at­tic.

From the in­side

Small holes of 15 to 50 mm. are drilled through the in­side wall fin­ish and the in­su­la­tion is blown or in­jected di­rectly into the wall. The holes must then be com­pletely plugged and sealed.

If you must re­place or re-cover the in­te­rior fin­ish, it should be pos­si­ble to drill the holes, blow in or in­ject the in­su­la­tion, in­stall a well-sealed air and vapour bar­rier on top of the old in­te­rior wall, ap­ply new dry­wall and fin­ish.

From the out­side

Most types of ex­te­rior sid­ing can be drilled, lifted or re­moved to ac­cess the stud wall be­hind. In some cases, brick sid­ing can have sin­gle bricks tem­po­rar­ily re­moved leav­ing suf­fi­cient space to re­pair holes in the sheath­ing. Ide­ally, two stud spa­ces can be filled from one brick space, though each stud space may re­quire two or more holes with this method. Do not in­su­late the drainage cav­ity be­tween the brick ve­neer and the stud walls. Make sure the in­staller patches the holes sec­tion by sec­tion rather than leav­ing them all un­til the end to avoid wa­ter en­try if a storm oc­curs.

From the base­ment/at­tic

This can be the eas­i­est ap­proach if ac­cess can be gained and if the cav­ity is open from top to bot­tom such as with bal­loon frame con­struc­tion. All stud spa­ces need to be filled, but there should be al­lowance for win­dows and doors, fire stops, cross braces and other ob­struc­tions in the wall cav­ity. The con­trac­tor will check to see if the wall should be filled from the top, bot­tom or both, de­pend­ing on ob­struc­tions. Af­ter the wall is filled, en­sure that the ac­cess holes are tightly sealed.

In­su­lat­ing the in­te­rior in­volves in­su­lat­ing the old wall, ex­tend­ing the elec­tri­cal boxes, ap­ply­ing the air and vapour bar­rier, crossstrap­ping, hor­i­zon­tal in­su­la­tion be­tween the strap­ping.

Ren­o­vat­ing the in­te­rior

If your plans in­volve ex­ten­sive ren­o­va­tion, you have two op­tions: you can re­build the ex­ist­ing wall or build a new wall on the in­side of an ex­ist­ing one.

Re­move the ex­ist­ing wall board or plas­ter from a wood frame wall, add or up­grade the ex­ist­ing wall cav­ity in­su­la­tion and then in­stall the vapour bar­rier, new dry­wall and fin­ish.

Al­ter­na­tively, af­ter fill­ing the cav­ity with in­su­la­tion, screw or nail the rigid foam board di­rectly to the ex­posed studs. Foam board ma­te­ri­als, with their high RSI (R) value, use less in­te­rior space and pro­vide a ther­mal break. De­pend­ing on the type and thick­ness of the foam board used, ei­ther seal the foam board to act as a vapour bar­rier or in­stall an ap­proved vapour bar­rier.

If you are con­sid­er­ing hav­ing spray-foam in­stalled, there are two ba­sic tech­niques – one that uses low-den­sity spray foam and the other, high-den­sity spray foam.

For low-den­sity ap­pli­ca­tions, you can choose to re­move any ex­ist­ing wall cav­ity in­su­la­tion and fill the cav­ity or bet­ter yet, strap the wall and then fill the full, deeper space. The low-den­sity foam will act as an air bar­rier, but you will have to in­stall an ad­di­tional vapour bar­rier be­fore cov­er­ing the wall with dry­wall and fin­ish­ing.

For high-den­sity spray foam, first strap the wall to cre­ate a deeper cav­ity. Then spray a con­tin­u­ous layer of foam (min­i­mum 50 mm [2 in.]) against the ex­te­rior sheath­ing and also cover the fram­ing mem­bers. Fill the rest of the cav­ity with your choice of in­su­la­tion ( e. g. low-den­sity spray foam, glass, min­eral or cel­lu­lose fi­bre).

Build a new wall on the in­side of an ex­ist­ing one

With both wood frame and ma­sonry walls, you can build a new in­su­lated wall onto the ex­ist­ing one.

The new frame wall can be in­stalled any dis­tance from the old wall as long as all cav­i­ties are filled with in­su­la­tion.

If you en­sure that a new, wellsealed vapour bar­rier is in­stalled, there is no need to re­move or dam­age any ex­ist­ing vapour bar­rier.

In both op­tions noted above, fol­low the rel­e­vant part of the in­struc­tions for in­su­lat­ing a base­ment from the in­side.

This in­cludes seal­ing air leaks, fram­ing the new wall, fram­ing around win­dow and door open­ings, in­su­lat­ing (ide­ally in two lay­ers so there are no gaps), in­stalling an air and vapour bar­rier, and ap­ply­ing the new fin­ish.

FILL­ING THE GAPS: Spray­ing foam in­su­la­tion is a good way to fill gaps while in other spa­ces, rigid in­su­la­tion or batts will do the job.

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