Any structural engineers? Second story wooden extension...
Discussion
I'm looking for a bit of knowledge and a sounding board! haha I can find very little info about second story wooden extensions...
I'm planning to extend the below property (STPP), creating a 4m x 3m second story extension as an 'infill' in the area above the single story pitched roof/rendered area. Let's just imagine for a second PP isn't an issue.
To get all Kevin McCloud for minute, the building isn't historic but it does have some history having been an coach house in the 1890s, then a workshop through the 40s/50's before eventually being turned into a small property. I love that you can see it's previous uses and I will be doing my best to accentuate those features in an extensive but sympathetic renovation. So when planning the extension it was very important to me that I add to the property and not destroy it's history. Externally I wanted the new part to fit with the old part softly but be distinctly different. My general felling was that a wooden cladding would be a soft alternative, which is both different to bare brick and the rendered area.
I then went a step further and thought, what if I build this structure completely from wood? I was thinking, removing ~1/2 tone of welsh slate and replacing with a low weight i-beams for floor and roof (the roof will need to be flat rather than pitched, 1) to minimize total high for light reasons and 2) I would like to have a lantern roof light.) Rubber roof, wood batten walls filled with Kingspan, sealed then then clad externally. Would the weight saving be enough to not require underpinning the foundations? (i'm not expecting a actual answer to that haha, just theoretically) Or is there a building code which says 'doesn't matter how much it weights, you need foundations of X depth if 2 storys...'? I'm assuming that the foundations are the same for the font part of the property (2 stories) as the rear (1 story) as I am confident they were built at the same time. This as been confirmed by old maps as well as the rear part has a capped chimney which is of the same construction as the front part of the house.
I know that you may get issues with lending due to 'non-standard construction' but the extension should be less than 25% of the property so not sure this would be an issue...?
What other negatives would there be for taking this approach?
I'm planning to extend the below property (STPP), creating a 4m x 3m second story extension as an 'infill' in the area above the single story pitched roof/rendered area. Let's just imagine for a second PP isn't an issue.
To get all Kevin McCloud for minute, the building isn't historic but it does have some history having been an coach house in the 1890s, then a workshop through the 40s/50's before eventually being turned into a small property. I love that you can see it's previous uses and I will be doing my best to accentuate those features in an extensive but sympathetic renovation. So when planning the extension it was very important to me that I add to the property and not destroy it's history. Externally I wanted the new part to fit with the old part softly but be distinctly different. My general felling was that a wooden cladding would be a soft alternative, which is both different to bare brick and the rendered area.
I then went a step further and thought, what if I build this structure completely from wood? I was thinking, removing ~1/2 tone of welsh slate and replacing with a low weight i-beams for floor and roof (the roof will need to be flat rather than pitched, 1) to minimize total high for light reasons and 2) I would like to have a lantern roof light.) Rubber roof, wood batten walls filled with Kingspan, sealed then then clad externally. Would the weight saving be enough to not require underpinning the foundations? (i'm not expecting a actual answer to that haha, just theoretically) Or is there a building code which says 'doesn't matter how much it weights, you need foundations of X depth if 2 storys...'? I'm assuming that the foundations are the same for the font part of the property (2 stories) as the rear (1 story) as I am confident they were built at the same time. This as been confirmed by old maps as well as the rear part has a capped chimney which is of the same construction as the front part of the house.
I know that you may get issues with lending due to 'non-standard construction' but the extension should be less than 25% of the property so not sure this would be an issue...?
What other negatives would there be for taking this approach?
I'm not a structural engineer, but I've designed and managed the construction of several such conversions/extensions in the past, in one of my former lives as Design & Tech Director of a timber frame company.
You need to know what you're doing with the detailing of the timber frame structure, but it's eminently possible.
You need to know what you're doing with the detailing of the timber frame structure, but it's eminently possible.
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