Converting Porch into room

[Bbp78]

Hi all, hopefully this is an appropriate place to post this as it’s not garage related, but I know how knowledgeable you all are and you have helped me in the past. I have a porch that was built in 1954 with my house. I demolished it a few months ago with the intention of building a room. I need to make it about 3 feet wider than the original existing concrete foundation. The slab has a block foundation that goes down to the frost line from what I can tell. I live outside Philadelphia, PA. My question is if there is another alternative to digging down to the frost line, pouring a footing and either laying block or forming and pouring concrete walls for the 3 foot extension? I was thinking about sonotubes and framing a floor over the existing foundation, but my concern is if I don’t do a full concrete foundation, will I have issues with animals wanting to get under this tiny “crawl space” or any other concerns I’m not thinking about? It’s not a very big addition, so I could definitely frame it with the sonotube piers, but do you guys think that’s a mistake. I’ve attached a few pictures showing the existing concrete foundation. Thanks in advance for any advice and guidance.

 

[kaehlin]

I think if it is attached to your house, you will need to follow building codes. I assume this means full foundation below the frost line, but you'll want to check for anything specific in your locale. Good luck, looks like a cool project.

 

[mike93lx]

Attached to the house means footings at the same depth but that doesn't necessarily mean full foundation.

Are you permitting this?

 

[Bbp78]

Thank you Mike and Kaehlin, I apologize I forgot to mention that I will be getting a permit. Maybe I should call and speak to the Building department to get there thoughts first. I have to submit drawings but wasn’t sure which foundation. If piers are allowed, do you guys see any issues going that route? I would block it off, but just wonder if it will be a headache down the road not doing the full foundation, etc. Thanks again

 

[joebass3]

Definitely would be easier with some piers and a beam on top if that would meet building code. Block it off to keep critters out and I think you'll be fine.

 

[Bbp78]

Thanks Joe, yeah I would like to keep it simpler. I built my shop 6 years ago and did the footings and block foundation myself, but would prefer not to on this if possible, even though this would be much smaller.

 

[jar944]

Doesn't look like you have enough elevation for piers.

 

[Natty Bumppo]

Think I would do the piers with a floor framed over the pad with one exception...I would do Techno-posts. No digging, no pouring a footer, no messing with rebar and cement, etc. No time spent with leveling the cement piers. And really, for the price of the tube, cement, rebar, and some kind of Simpson Strong Tie post base, a Techno-post isn't that much more expensive. If you factor in your time they are probably the same cost. A good company would be in and out of there in an hour. They would have the posts leveled for you. And you'd be building that same day.

 

[75gmck25]

We had a very similar project for our conversion of a screened side porch to a fully enclosed porch. I chose to demo everything, excavate and pour footings, then use concrete block, followed by conventional floor framing over a short conditioned crawl space. New porch is two stories, so it also connects to a bedroom on the 2nd floor. Crawl space was really useful for running plumbing and electrical. My architect also said I could have just done slab on grade, but I never got plans for that alternative.

A couple of questions/comments
- Since you don't know the depth of the footings under the existing slab, the city will probably want you to find out if you want to build on it. You may have to pay a certified engineer to verify and document what is under the slab and I don't know how much that will cost. For my porch footings I only had to verify I was pouring the footings on undisturbed soil and I think it cost about $500 to have an engineer come out and look at my hole in the ground. Quite a lot for a very short visit.

- Since I framed on a crawl space block wall, I had to use approved fastenings to connect the ledger board to the existing house (ledger lock threaded bolts? and some threaded tie bolts connected to the framing), and I had to use rebar to pin the new footings to the existing basement wall. The point is to ensure you don't ever have the porch shifting independently of the house.

- it doesn't look like you are close to a property line, but my porch was too close to meet current code. I had to apply for a variance to rebuild at the same distance from the lot line. I also got a weird city "engineer" who decided that I needed a fire-resistant wall assembly on that side because it was close to the lot line. He seemed to not understand that there was a driveway on the adjacent lot, so I was still a long way from any structure. However, my architect knew the code for a "fire-resistant wall assembly", so it turned out to be only a small change to the materials.

 

[d.mcfarland]

Honestly the $10,000 for digging a hole and doing blocks will be well worth it. Below frost line but doesn't have to be the same as original. Doing some proper water prevention like tile drain will prevent any movement.

Do it once and do it right I guess is my ultimate guidance.

 

[mike93lx]

frost line but doesn't have to be the same as original.

If it's attached, it needs to be at the same depth

 

[d.mcfarland]

If it's attached, it needs to be at the same depth

If the current porch didn't cause any damage in the last 71 years at a frost line depth, then an addition at or below that line likely will have the same results.

 

[mike93lx]

If the current porch didn't cause any damage in the last 71 years at a frost line depth, then an addition at or below that line likely will have the same results.

Doesn't change the requirements

 

[d.mcfarland]

Doesn't change the requirements

That's IF someone is permitting. I know the OP said they were, but I'm saying if not, there will be no harm done by not matching the original house footings.

 

[larry4406]

@Bbp78 which direction(s) are you increasing the foot print of the proposed build? You are limited by the window on the left, there is some margin to the right to the house corner. I am guessing perpendicular to the brick wall.

When we did the 8x16' kitchen extension on our house, we did a crawlspace with block walls while existing 8' tall basement foundation is poured concrete. The footings for the crawl space are below frost but nowhere as deep as the house foundation's original footings. The crawlspace footings are keyed and doweled into the house foundation and each block course has rebar doweled and epoxied into the house foundation.

Do you plan on having the flooring at the new room level with the first floor of the home or stepped down?

How are you accommodating the 2nd floor door that I am guessing went out on a roof deck?

 

[75gmck25]

The code here (Alexandria, VA) required footings to be a certain number of feet down to be below frost depth, but it did not have to match the existing house.

My basement has about a 7 foot ceiling, with block walls and a footing below it. The new crawlspace has a footing with five rows of block on top to get it to match the top of the house block wall. As I already mentioned, the new ledger board had to be attached to the ledger board on the house with approved fasteners, and rebar was epoxied into the existing basement wall so it extended out into the new footings. This was permitted, inspected and approved.

 

[JohnX14]

Is the slab in pics also the floor of the new living space? Basically you will build the walls on top of this exisitng foundation, there will be no floor joists? Doesn't look like there is height for floor joists. If that's the case, just dig down and pour a footing, block the foundation and pour a floor extension. Techno posts are not the right choice for this. It sits at ground level,