What is the best way to go about this?
I have some great insulation that I want to cut and size to fill a small
underground area that holds my sprinkler cut off handles.
I call it a vault, but it is simply a dirt hole with a piece of metal
around it to keep the dirt from falling inside, and a plastic lid.
Can I just put the insulation directly into the hole, or do I need to
put plastic over the lid, on top of the dirt, to keep it dry?
My feeling is that when the snow melts, it will dampen the insulation
and freeze it.
Also, could I just put the insulation inside of a plastic bag to keep it
dry, or will this defeat the purpose.
I know this is such a small thing, but it boggles my mind.
You do need to keep the insulation dry. It will work just as well
inside a plastic bag. How wll it works depends on your location. The
heat source in this case is the ground. If the ground under your
sprinkler valves freezes anyway then the insulation won't help you.
Most people drain their sprinkler system if it is in danger of
Unless the insulation extends down past the frost line it will do
little good. You mention snow and freeze. This requires you to
winterize the system. Turn off the water inside the house and blow
out the pipes with a compressor.
Why on earth you would ever need to "insulate" a winterized
lawn sprinkler system boggles the mind...
If you are concerned about snow melt/thaw cycles filling the
"vault" with water and doing some kind of damage then you
need to rebuild your "vault" so that it doesn't trap and pool
water... Some anally retentive people will dig the valve boxes
deeper than needed and place some gravel under where the
valves will be installed to allow for some drainage...
Adding insulation to such a vault will not prevent damage from
water getting in and freezing...
I believe the previous owners froze up one year, and hired a plumber to
extend the shut-off valve underneath the house. I don't worry about
that part freezing, but I worry about the short piece of pipe on the
outside leading to the inside.
It is hard to describe.
I did put a plastic bag underneath the lid so hopefully snow won't melt
and get inside.
It has been fine for five years without insulation, but a plumber
recently looked at it and suggested adding insulation.
The plumber is misguided and/or optimistic. Insulation will not
prevent pipes from freezing unless the insulation is trapping heat
from somewhere. You didn't mention where you're located, so it's
tough to know what sort of climate you have. What's your estimate of
the typical bad-cold-snap low temperature in your area?
It doesn't sound like you have a basement. If not, there is little
possibility that the foundation would lose enough heat that the
insulation could trap. Even if you did have a basement, you'd have to
have uninsulated foundation walls, the valve box would have to be
right next to the house, and the insulation would have to extend down
past the frost line on the exposed three sides to have much hope of
the insulation actually preventing a freeze.
A safer bet would be to install electrical heat trace tape with a
thermostatic control, but that obviously involves more work and
expense than throwing some insulation on top of the pipes. BTW, what
exactly do you mean when you said "I have some great insulation that I
want to cut and size"? Is it fiberglass or rigid foam insulation?
Frankly, if your pipes have been blown out it's unlikely that there
will be a problem. A pipe won't rupture unless water is filling the
pipe when it freezes. If the pipe isn't full, it's very unlikely that
freezing would damage it.
It isn't rocket science to correctly drain a sprinkler system and once
done there is no need to insulate anything. I agree with those that
have said any attempt at insulating the valve box is a waste of
time. Insulation only slows the heat transfer, it doesn't stop it.
If the frost line extends down a foot or more in your area, then it's
going to freeze with or without insulation.
The solution is to blow it out correctly. It sounds like the plumber
might be concerned about the one section of pipe that heads back to
the house and is on the other side of the blow out port from the
sprinklers. If so, I'd put a T with a drain plug in the line. After
blowing it out, you can open the drain plug. That will work if the
line slopes in the right direction, which it should if the install was
done correctly. If it doesn't then I'd fix it by repitching that
piece of pipe. Or wait and see if it does freeze and bust and then
just replace it once correctly and be done with it. But I don't see
what the issue is that's specific to the valve box freezing which
should just be blown out.
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