Demolishing/rebuilding half of a semi-detached home

[morrowd]

We are thinking of demolishing part of our half of a single-story semi-detached home and rebuilding it with a second story and a basement under our half. Presently both halves have only a crawlspace. I expect there is limestone to excavate. The roof of the portion of the structure to be demolished and rebuilt has a gable roof with the ridge running along the property line. Is our idea possible? What special challenges are we up against?

[mx2]

Can you hare more details? The crawlspace hints at a wood frame structure, at least a wood framed floor system. Limestone is a problem in terms of excavating with an existing structure to remain. You'll need some heavy equipment with room to maneuver. I wonder about your zoning since it's some form of zero lot coverage and often new ordinances shy away, or expand on this notion. And depending on the wall system, a second floor may require additional structure which ultimately when you think about it, you might be better off re-building the half from ground up. I'm thinking (without enough info) that to excavate with existing partial structure in place could prove to be difficult and would be easier if there was nothing there. Then make sure zoning regulations will allow what you seek to do. Then if (and I emphasize if) the existing structure cannot support a second floor and additional footings, columns and beams are required and you obviously need to re-roof I just see it as being easier, better and possibly cheaper to demolish the entire half and re-build it exactly the way you would want. But this is all conjecture because I have no idea what the conditions are...so forget what I said. Got any pictures?

mx2

[morrowd]

Sorry, I should have been clearer. We [i]do[/i] want to demolish our half and rebuild from the ground up. My concern really is (i) how to support the neighbour's half of a gable roof system while we tear down and rebuild our half, and (ii) how to excavate for the basement on our half without causing structural damage to the neighbour's house. By way of overall context, the structure I'm referring to is a rear addition (circa 1900) to the sunny end of a a row of cottages dating back to about 1870. There is a good-sized side-yard that should give heavy equipment enough room to get around. The house is a wood-frame structure, presently with a 2x4 party wall. The crawlspace is inaccessable, so I don't know what (if anything) is supporting the party wall. But an exploratory hole in the floor on my side revealed joists sitting on soil. My guess is a rubble foundation around the perimeter but as I say, that's just a guess. As for the roof, presently there is a common attic with no firewall. No truss system. I'm contemplating a saltbox-type roof, with the larger slope representing the neighbour's, and part of our proposed, roof so as to not block sunlight to our ajoining neighbours to the north. Hopefully that helps to clarify the picture a bit.

[mx2]

Thanks for pic and explanation...now it's getting really interesting. Is that part of the home we see further in the background a shed roof or another gable? I assume you want to demolish that "wing" right? I'm not suprised the parti wall does not penetrate to the roof deck as it's simply easier to fake it which means I suspect you're right also that it does not go down to a footing either. It's definitely a fire hazard in that sense. Regardless, it's a big project you've decided to take on...congratulations! How exciting.

Well, the first thing that struck me was that down here in Florida (I never did ask; what region is this house located?) wood framed houses tend to rot very quickly especially if not well vented and we also have limestone which indicates the water table may not be too far away, am I right? Regardless, in a way the limestone is a blessing and a curse. It's stable enought to hold the existing rather well in place while digging up the adjacent space and in fact they have this water/vacuum thingie (very techincal term) that wets, loosens and sucks away the limestone. But I would be concerned about moisture resistance for the new structure. Some form of moisture resistant barrier must be installed prior to laying any slabs or flooring down. In fact I imagine a split floor plan (reduce the excavating) and its bascially all in concrete (like a bath tub) then build a wood frame structure above that. Are there any other conditions nearby to be concerned about? Lake, canal, river, beach etc? If so you may need a mat foundation. At any rate...I think, I know it can be done but ultimately it comes down to is it worth it? I recommend you hire an architect to develop a schematic design for you and then take it to a local builder and ask for a preliminary cost estimate.

Overall I like your ideas. The saltbox roof remains in context and depending on your program (space requirements) I see some interesting play with windows, patios and /or doors at the second floor. Spatially I love vertical spaces and who knows what else could be brought into this...but it mostly depends on what you want. That's another story. It's getting late...long day tomorrow. Hope this helps a little.

mx2

[mx2]

Oh nearly forgot, as far as supporting the adjacent gable roof during construction it's really the contractor's option but what I've seen done is they build additional supports near the point where the roof will be removed before demolishing. The wood deck helps hold it al together, despite not being trusses, the wood member frames work as a system with the plywood deck. I don't think it will be too much of a problem but ultimately that's where *I* would defer the liability to the contractor and ask them to suggest to me what do they recommend. Litigation is a terrible thing....which leads me to the correct answer: get an engineer to check it out ahead of time. A structural inspection is worth its weight in gold. In fact now that I think about it (almost asleep now) everything I said depends on an engineer walking the site to verify conditions. I'm thining about the ridge beam, other beams and columns. It's impossible to tell without seeing it...so start there. My 3 cents. Invoice is in the mail...



mx2