Go Back  DoItYourself.com Community Forums > Exterior Improvement Center > Decks, Patios, Porches, Walkways, Driveways, Stairs, Steps and Docks
Reload this Page >

excavating under existing three-season porch - insulation and frost question

excavating under existing three-season porch - insulation and frost question


Old 08-03-13, 07:33 PM
Thread Starter
Join Date: Aug 2013
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
excavating under existing three-season porch - insulation and frost question

I recently dug out the crawlspace under my 3-season porch (changing it from a 3' high crawlspace to a 6' high storage area) but have been reading mixed advice regarding insulating the now-exposed exterior wall of my basement. By removing 3' of soil from around the basement (though I'm still about 3' above the footings) I've lost the insulation the dirt was providing. The exterior wall has 2" rigid insulation already but I'd like to add more on top to compensate for the lost dirt. Questions: by removing the dirt, have I created a problem with regards to frost, as the rigid insulation I have is no longer buried deep? If I add more insulation to compensate for the lost dirt, do I need to dig down another 2' to bury it, even though the existing insulation is now only an inch or two below grade?
Sponsored Links
Old 08-04-13, 05:29 AM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 46,427
Received 156 Votes on 138 Posts
Welcome to the forums!

Isn't there still dirt on the outside of the foundation? Or am I mis understanding what you are doing?
Old 08-04-13, 08:37 AM
Thread Starter
Join Date: Aug 2013
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
under porch excavation

Thanks for the reply and the welcome - I may not have been clear in my posting. To clarify, I have a three season covered elevated porch, under which was simply dirt. I dug out the dirt to a depth of about 6' so as to have a storage place. I am therefore excavating next to my foundation, but not down to it; I stopped excavation about 3-4' above the bottom of the foundation (in other words, my basement floor is about 3-4' below the excavated level of the new storage area).

With 3-4' of dirt still covering the bottom of the foundation I'm not too worried about frost (particularly since the storage area is also covered by the three-season porch above), but I've also exposed the 2" rigid insulation along the basement wall exterior and I've read that this should be down at least 2' under the soil. Do I dig down another 2' and add in another layer of rigid insulation? Or would it be sufficient to lay down horizontally some rigid insulation about 1-2" under the dirt?

My apologies if I'm not making this problem clear - basically I'm worried about 1) frost and 2) replacing the insulating effect lost by the removal of the dirt.
Old 08-05-13, 03:06 PM
Join Date: Oct 2008
Location: New England
Posts: 10,481
Received 31 Votes on 28 Posts
Hi can't do,
let's see if we can sort out what you have.
Is this porch resting on foundation walls that extend down about 6 feet into the ground and are built on top of a footing at the bottom?

Is the basement area open to this area under the porch or will you be cutting a hole through the basement wall?

Just having trouble figuring out what you have.
And what is your climate, any frost?

Old 08-08-13, 04:56 PM
Join Date: May 2013
Location: USA
Posts: 12
Received 0 Votes on 0 Posts
maybe this helps

Sounds to me like he has a 3 season/patio room built onto the outside of his house like a deck that has been closed in. The area under this "attached" room is what I think he's asking about. The way you described the foundation I believe I would dig down and install insulation below grade to match the way it was before you excavated the area. But that's just my opinion and I've been known to over do it at times.
Old 08-15-13, 07:04 PM
Thread Starter
Join Date: Aug 2013
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
yes, you've got it right

porch rests on pillars which go down 10ft to footings. Have no intention of connecting basement to the now-excavated area under the porch (it's for storage only). Having read the replies (and some other bits elsewhere), will now dig down another 5-6" and bury two sheets of 2" rigid insulation perpendicular to the outside wall of my basement. This will (hopefully) stop any frost penetration (even though the bottom of the foundation is about 4' further down).

Question: how far our from the wall should this rigid insulation go? The sheets are 4' wide - that seems far enough I would think.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title: