Expert: Ted Barnhill (Principal, Design45 LLC) - 8/2/2009

Question
We just converted our 10' x 35' patio and want to make a sun room.  It's about 4' feet above the ground and is covered by the original roof. The 10 feet span is supported by four feet tall 4 x 4's, which sit on concrete footing. Seven of which run across the 35 feet front. The house and deck is 3 years old and the patio flooring is constructed of 2 x 6 pressure treated wood. On top of the flooring the seven (plus 1 on the narrow side) 4 x 4's 'continue up' to support the overhang from a truss. The railing and a 'door opening' was in between. No permit is needed where we live.

We planned on adding 8 windows on the long side (360 lbs) and 2 windows on the short side (100 lbs) plus a new door.  We tore out the rails and the new 'pressure treated' framing weighs about 300 lbs (6 lbs per 2x4) and will probably dry out lighter.  The outside and inside OSB which we put up is about 600 lbs. Now, I (the wife) am worried sick about all this weight - worried enough to have my husband concerned.

We also plan to put up tar paper and OSB over the existing flooring for another 600 lbs, plus vinyl sheets or laminate Wood flooring. (max 360 lbs) and outside vinyl siding (maybe 100 lbs) When all would be said and done we might have increased the weight of the structure by 2100 lbs from the previous weight.

Will we need more support (from the ground up) under this 350 sq feet area and if so, suggestions - what and where ?   Any help is greatly appreciated.  

Answer
Kate,

Your newly-built home, if built to code, would have been engineered for a dead load of 10-20 lbs/sq. ft. and a live load of 30-40 lbs/sq. ft, for the floor area only, not including roof loads.  These ranges would include your 350 porch/deck area also.  The loads that you propose (which are dead loads) amount to less than 10 lbs./sq. ft.  Based on this, I would not be concerned about the additional load of enclosing the space.

However, as you mentioned that permits are not required in your area, you may have doubts whether your home was engineered or built to current code.  If so, it would be well worth it to have an engineer look at your structure, especially the footings.  

Ted Barnhill