porch support

mcn520 · 07-12-2011, 09:27 AM

I have a cottage with a porch that extends out (the end being over the water) approx 8'x8'.
it only has three 4x4 posts underneath spaced intermittently and sitting on rock.
I want to properly support this porch and was thinking of nailing (2) 2x6 together to span the length and putting it at the midpoint with 4x4 posts underneath that for support.
any suggestions or corrections would be appreciated. thanks

Steveo · 07-12-2011, 11:59 AM

The rule of thump for a cantilever (which is what you are making) is 2/3rds by 1/3rd. That means put the cross beam 2/3 length out from house with 1/3 length overhanging.

Rattlesnake Guy · 07-12-2011, 11:00 PM

How big are the rafters on this 8 x 8 porch?

Do you have the option of going further out as suggested above or are you limited to only going to the center?

Think of the design like the nails will rust away. Compressive loads are much safer. (Beam over the post or Notch in the post.) Galvanized bolts are better than nails at key points. Hangers may be required by code for certain wood wood connections.

The problem with putting the beam at the center line is that when 6 of your friends line up to look at the lake on the edge, their total weight will be lifting on the house side. If that side can go up somehow, the lake side will go down like a sea saw in the playground.

If you put diagonal supports from the bottom of the post to the outside of the porch and your friends line up, the force will now try to pull the porch away from the house. (Up and away)

The further out you can touch the ground the more reduced the physics of trying to turn the porch into a swim platform.

Onshore · 07-13-2011, 07:29 AM

Please read this section of RSA 482-A, the Wetlands Act, found here.

http://www.gencourt.state.nh.us/rsa/...A/482-A-26.htm

It does not prohibit your ability to make repairs to your home but the language of the law is rather strict and gives no discretion to the Dept of Environmental Services if work does not otherwise comply with the provisions therein.

If you need to place supports on the bank or lake you will need a Wetlands Permit.

mcn520 · 07-13-2011, 08:29 AM

thanks for the info. much appreciated
the porch currently has three 4x4 posts underneath it so i won't be installing new ones. i will just be supporting the porch properly with the three posts under a cross beam.
i will use the 2/3 by 1/3 rule.
i also read the law on the suggestion of shore things and i believe i will be in compliance.
thank you

DickR · 07-13-2011, 08:55 AM

In addition to providing proper vertical support away from the house, you should review how the deck is attached to the house. Over the decades there have been far too many incidents of decks separating catastrophically from the house, resulting in injury and even death. Some of these failures are due to deck ledgers simply nailed into the house structure and subject to pullout, and others have resulted from inadequate flashing of the ledger attachment, allowing rain into the structure with ensuing rot.

The latest version of the IRC (2009) building code now covers prescriptive detail for deck attachment. While your existing deck is grandfathered, you owe it to yourself and anyone who uses the deck to check that attachment and beef it up as required. Considering your description of how the deck is supported at present, it wouldn't surprise me if the whole thing is another deck failure waiting to happen.

07-12-2011, 09:27 AM	#1
mcn520 Junior Member Join Date: Aug 2009 Posts: 8 Thanks: 0 Thanked 0 Times in 0 Posts	porch support I have a cottage with a porch that extends out (the end being over the water) approx 8'x8'. it only has three 4x4 posts underneath spaced intermittently and sitting on rock. I want to properly support this porch and was thinking of nailing (2) 2x6 together to span the length and putting it at the midpoint with 4x4 posts underneath that for support. any suggestions or corrections would be appreciated. thanks

07-12-2011, 11:59 AM	#2
Steveo Senior Member Join Date: Apr 2004 Posts: 523 Thanks: 47 Thanked 123 Times in 63 Posts	Cantilever The rule of thump for a cantilever (which is what you are making) is 2/3rds by 1/3rd. That means put the cross beam 2/3 length out from house with 1/3 length overhanging.

07-12-2011, 11:00 PM	#3
Rattlesnake Guy Senior Member Join Date: Sep 2004 Posts: 1,254 Thanks: 423 Thanked 366 Times in 175 Posts	How big are the rafters on this 8 x 8 porch? Do you have the option of going further out as suggested above or are you limited to only going to the center? Think of the design like the nails will rust away. Compressive loads are much safer. (Beam over the post or Notch in the post.) Galvanized bolts are better than nails at key points. Hangers may be required by code for certain wood wood connections. The problem with putting the beam at the center line is that when 6 of your friends line up to look at the lake on the edge, their total weight will be lifting on the house side. If that side can go up somehow, the lake side will go down like a sea saw in the playground. If you put diagonal supports from the bottom of the post to the outside of the porch and your friends line up, the force will now try to pull the porch away from the house. (Up and away) The further out you can touch the ground the more reduced the physics of trying to turn the porch into a swim platform.

07-13-2011, 07:29 AM	#4
Onshore Senior Member Join Date: Apr 2004 Posts: 502 Thanks: 12 Thanked 423 Times in 145 Posts	Please read this section of RSA 482-A, the Wetlands Act, found here. http://www.gencourt.state.nh.us/rsa/...A/482-A-26.htm It does not prohibit your ability to make repairs to your home but the language of the law is rather strict and gives no discretion to the Dept of Environmental Services if work does not otherwise comply with the provisions therein. If you need to place supports on the bank or lake you will need a Wetlands Permit.

07-13-2011, 08:29 AM	#5
mcn520 Junior Member Join Date: Aug 2009 Posts: 8 Thanks: 0 Thanked 0 Times in 0 Posts	thanks for the info. much appreciated the porch currently has three 4x4 posts underneath it so i won't be installing new ones. i will just be supporting the porch properly with the three posts under a cross beam. i will use the 2/3 by 1/3 rule. i also read the law on the suggestion of shore things and i believe i will be in compliance. thank you

07-13-2011, 08:55 AM	#6
DickR Senior Member Join Date: Apr 2008 Location: Moultonborough Posts: 749 Thanks: 4 Thanked 259 Times in 171 Posts	In addition to providing proper vertical support away from the house, you should review how the deck is attached to the house. Over the decades there have been far too many incidents of decks separating catastrophically from the house, resulting in injury and even death. Some of these failures are due to deck ledgers simply nailed into the house structure and subject to pullout, and others have resulted from inadequate flashing of the ledger attachment, allowing rain into the structure with ensuing rot. The latest version of the IRC (2009) building code now covers prescriptive detail for deck attachment. While your existing deck is grandfathered, you owe it to yourself and anyone who uses the deck to check that attachment and beef it up as required. Considering your description of how the deck is supported at present, it wouldn't surprise me if the whole thing is another deck failure waiting to happen.