Adding insulation to house attics

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Adding insulation to house attics

Shirtliffe, C. J.

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Wlb8

.

BUILDING

PRACTICE,

--OTE

A Y

ADDING INSULATION

TO

Division of Building Research National Research Council of Canada

ADDING INSULATION

TO

by

C . J . Shirtliffe

Thousands o f Canadians are contemplating adding i n s u l a t i o n to the a t t i c s of t h e i r homes, but require f u r t h e r information on how to select the most suitable type, how much it will _{c o s t , and how}

to apply it.

This

on

can be found in reference (1) and

the

of

in

7 September 1 9 7 4 .

A t t i c s may b e insulated with e i t h e r l o o s e - f i l l i n s u l a t i o n s or b a t t - t y p e i n s u l a t i o n s . Loose-fill i n s u l a t i o n s may be applied by pouring and then l e v e l i n g , or with a blower. Contractors normally use batt- or blowing-type insulation in new construction and

blowing- or pouring- type i n s u l a t i o n when adding i n s u l a t i o n to an e x i s t i n g a t t i c . These types are used because they m i n i m i z e t h e total installed c o s t . Homeowners generally do n o t have t h e equip- ment necessary for blowing so must use b a t t

or

Thermal i n s u l a t i o n s can be compared in term of t h e installed c o s t of t h e i n s u l a t i o n necessary' to provide one u n i t o f thermal resistance over a one s q u a r e foot area. T h i s is calculated from

the c o s t _{o f a square f o o t of i n s u l a t i o n d i v i d e d by i t s thermal}

r e s i s t a n c e , i . c . , R-factor.

'the It-factor is p r i n t e d

on

is

f o r

t h i c k n c s s c s on bags of p o u r i n g a n d blowing insulation. Som manu- f : ~ c t u r c r s s i n q ~ l y list t h e R-factor f o r one inch of insulation. Wllcrc no i tlforn~;~t ion is provided, the thermal resistance per inch

c a n hc dctcrmincd as the reciprocal of thermal c o n d u c t i v i t y

( k vi~lltcs) l i s t e d

in

In any c i t y , the price of a particular i n s u l a t i o n can

vary

by at Icast 20% from one supplier t o anather. It can a l s o vary w i t h q u a n t i t y . I t is desirable to compare the p r i c e s

of

a l l

insulations on the same general b a s i s -

The

can

These

on

.

of

of

TABLE I

UNINSTALLED COST

[IN

VARIOUS IMSULATfONS

(per unit R-factor f a r square foot area)

Batts

-

wool*

-

t

(S.E.)**

Where insulation is being added to an a t t i c , b a t t s without medranes, called "friction fit" b a t t s

,

This method can increase the potential for f i ~ e to

spread especially

when

over

The f i g u r e s given in Table I can be

used

of

of i n s u l a t i o n in

an

a t t i c .

Far

example, u s i n g g l a s s fibre b a t t s t o increase the R-factor by 14 units, from the normal value

of

R-24, which

slightly below the most economical thickness for

mst

would

i , e . ,

R

$201 -60. Some p o i n t s to consider when instal l i n g insulation are:

(1) Walk

only on

or

(2) Protect loose, granular insulation

from

drifting

use adequately secured batt insulation a t such locations. (3) Ensure that s o f f i t vents do not become blocked and that a i r

passages are provided through to the a t t i c space. One method

to

_maximum

space between t h e top

of

and

(43 Insulate and weatherstrip t h e a t t i c access door and t i g h t l y

f i l l gaps around chimneys and a t concrete party walls with noncombustible materials. Locate and seal openings where plumbing or electrical

wires

reduce heat and air leakage.

(53 Ensure that exhaust fan ducts have t i g h t l y seafed joints, extend completely to the _{outside, and are insulated.}

Reference

(1) Stephenson,

D.

for Walls and Ibofs. National Research Council

of

No,