insulation [RE-wrenches]

[Peter Talmage]

Dear Mark,

Dry pine or spruce has an R value of about 1 per inch.
 A 4" wood roof with tar paper and shingles including
the interior air film would have a total R value
approaching 6. (This sounds like one of those "energy
efficient" log homes.)  Add insulation in this case ?
--- best invetment they can make. A 1000 square foot
roof with R-6 and a temp difference of 50 from inside
to outside, (very common in winter up here in the
north) looses 8,300 BTU per hour. In a day that's
200,000 Btu or about 2.1 gallons of fuel oil
considering the average total efficiency of your
typical heating system of around 70%. Increasing the R
value by 11 reduces that daily oil consumption by
about 1.3 gallons. Assume oil is $1.50 per gallon that
means a savings of almost $2 per day. Depending how
long the heating season is the savings could be in the
hundreds of $ per season. In the hot months the house
will be cooler and will require less air conditioning,
(if used). Now if oil or other fuels go up in price as
all of us know they will -----

Yours,  Peter Talmage

--- Mark Downing <solarman4 at yahoo.com> wrote:
> Knowing that some of the people here are involved in
> solar heating, I
> thought maybe I could get some good info here.
> 
> Given a shingled roof consisting structurally of a
> solid 4" of wood
> with tar paper and shingles on top, can anyone give
> a guess as to the R
> value afforded by the wood?  (The wood side is
> visible to the occupied
> space.  The roof in question is a 3 or 4 pitch roof
> of approx 50' by
> 100'.)
> 
> The roof is to be reshingled, and "the powers that
> be" are questioning
> whether it is worthwhile to add insulation that
> would add an R factor
> of 11.  To me, it's a no-brainer.  However, they are
> wanting someone
> knowlegable to assure them that they will realize a
> X% savings on
> heating/cooling.  (The old payback question.)
> 
> If anyone can give a clue as to the R value of the
> existing roof, and
> some educated guess as to the % savings, I would
> love to hear from you.
> 
> Mark Downing, Hurshtown Alternative Power
> 
> 
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