T shape house Q

[UK4X4]

based on the 20ft 1 1/2 story, 40 ft long with a 10ft wide porch extension, the extension being 16ft wide

I have two concerns, roof can I simply T the roof design and leave all open or will I need some tie ins
ie a truss of beam to span between the two walls of the 40ft side and back to the rear wall ?

I have no issues doing this as I was going to add some big timber features anyway.

Inside the main structure is a 12ft wide loft either side and a 1/2 width walkway leaving a 20ft x 16ft open to ceiling "great room" which includes the extension area.



The second is in regards to the basement, I'd prefer to do a rectangular 40ft X 30ft concrete walk in, but how do you build a waterproof roof below the decks either side ?

As a T basement adds cost for no real benefit and less usable space.

The basement would have a wall at the 20ft wide point to support the main structure

Here's a sketch up, the grey areas are my concern




In this one I used the bump out, pretty sure I need a 4ft knee wall or structure to support across at the 20ft width line, ie to cross the 16ft missing wall
think of a triangulated zig zag truss in 6" square with 6" SQ posts either side .


This roof is simpler but not as aesthetic, but is it still possible to do basicly using the original plans........

as a note the plot is long across the mountain and the great room would overlook the Colorado river valley

In both design's a central pillar would go from the floor to ridge 12 ft in from both ends

[John Raabe]

I like your first diagram. I think I would support the roof loads by either doing a truss package (engineering by the truss Co.), or install a structural ridge beam with support posts to basement footings. I would have the basement outline follow the heated floor area (in a "T" shape) and do the porch supports on independent piers. This eliminates lots of potential problems.

[UK4X4]

So a T basement would be the only real way of doing this ?

Ref roof  so a supported ridge would suit me, I like the idea of some heavy timbers basement supported through to the roof ridge
even some heavy trusses in the extension would work

but trusses in the main house would not as we want usable loft space both sides.

I was thinking along the lines of these in the extension back to where the extension meets the house, these are from my UK house where I took out the ceilings in my standard 100 year old box house. 2off 2x12" and a 6" x 6" upright to the original beam

[John Raabe]

Yes, those king post supports could work well again. Have someone check the sizing for your snow and wind loads.

RE: Foundation, It is not that a full perimeter basement couldn't be done, but it is much more complex and all the details have to be done correctly and stay waterproof over many years in all weather conditions. Decks exposed to outdoor weather are best done as free draining rather than as bathtubs, IMHO.