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Building Homes or Extensions/Room extension with 3 season porch below

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Expert: - 8/21/2011


Question
area for addition
area for addition
We live in northern Minnesota and would like to extend our livingroom/kitchen approximately 17' out from the existing house and 27' across. #our current home size is 28'x38'# We would be building over a walkout basement and enclosing underneath for a 3 season porch. What type of support would we need to ensure the addition does not separate from the existing house? What type of beam would give us the best support. What type of supports and how many would be required?

Answer
Hi Neva, considering the winters in your area you will need a foundation whose footing is below the frostline and designed for your local soil conditions.  Normally the footing should be two feet wide and a foot thick with reinforcing steel but you will need an engineer in your area to determine that for sure.  As far as the supports go it depends on how you want to build your porch.   Posts at 8 foot intervals will require a minimum header size of 4x8, I use the rule of thumb of one inch of beam thickness per foot of span so ten foot spans would have 4x10 headers etc.  Floor joists that span 17 feet will probably have to be engineered LVLs 1 3/4" x 16" or wood I-Beams but again you will need an engineer to finalize your exact requirements based on roof loads needed for your area for snow.  A ledger board will have to be attached to your existing wall to support the floor joist system and this attachment will depend on your existing wall construction and existing floor system of the house, it may be as simple as lag bolting  the ledger directly to the existing rim joist of the house.  All in all, if the foundation is done properly you won't need to worry about separation.  Get a local engineer involved early so that when you take your plans into the building department all the necessary engineering is in place for you to obtain your building permit. I hope this info helps please feel free to write again regarding this or other matters, sincerely Bruce Johnson..bejohnsonconsulting.com
    Questioner's Rating
    Rating(1-10)Knowledgeability = 10Clarity of Response = 10Politeness = 10
    CommentThank you very much, I will pass this information on to my husband.


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Bruce E. Johnson

Expertise

I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.

Experience

Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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