Insulation for basement-which R-value should I purchase

yummy mummy

I will be purchasing some insulation for my basement.
2X4 construction.

When I purchase the insulation, do I need to get the top R-value for best performance or is there a standard one for basement that will suffice?

Also, vapor barrier, which would I purchase 4 or 6 mil. Or does it really matter?


Thanks!

AtlanticWBConst.

For 2x4 framing you need to use R-13.

(The next step up is R-19, of which you would need 2x6 framing to accomodate it. This, you NEVER see in basements)

Use 6 mill Poly for the vapor barrier.

__________________
- Build Well -

yummy mummy

Thanks very much Atlantic.

I will do as you say.


One more question, if I may.

Do I need to insulate the interior walls?

concretemasonry

If you did't insulate all the exterior walls, your basement area is really not a insulated, conditioned space. In that case, your finished room is an uninsulated or partially insulated "island". I would insulate the remaining walls to separate yourself from the unconditioned (temperature and humidity) space. - This a problem with the idea of finishing off the interior or semi-exterior walls of a small space in a home.

Don't ask me what to do if you do not have a door between the upstairs and downstairs, or heaven forbid, a split ranch or a split entry.

If you are in an area that thinks there is a "magic" line around the basement at ground level, it gets more complicated.

AtlanticWBConst.

You need to insulate all exterior walls that are facing an unheated/cold area.
Any interior walls that are not facing (in your case) exterior feezewalls, do not need to be insulated.
(The exception to this is if you have a bathroom. It is best to insulate bathroom walls for sound purposes)

When insulating, you are creating what is called a 'heat envelope'. The inside of this 'envelope' is your living space. You want there to be a complete 'seal' of insulation around that 'envelope'.
Any walls INSIDE of that 'envelope' do not require insulation, if they are not part of what makes up the 'envelope'.

__________________
- Build Well -

concretemasonry

Atlantic--I agree with the concept of insulation an exterior envelope (no matter what method is used). That eliminates the question of what to do with the rest of the inteior walls.

You do the same thing when you build above grade, except you need far more insulation for the envelope because it is above grade.

Too often people insulate/finish a basement in piecemeal fashion.

yummy mummy

Thanks Atlantic and concretemasonry.

I have no bathroom in the basement. I understand completely the explanation of the "envelope", therefore, I will not insulate the interior walls.

thanks a bunch.