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rwiens

05:28AM | 04/27/04
Member Since: 08/13/01
13 lifetime posts
Bvtools
I am planning to build a deck on grade by laying 2x4s on the flat to act as 'beams' and then running joists over these. The question is what to put the 2x4s on: I think the two options are crushed stone or compacted aggregate/stone dust. The crushed stone will give better drainage, but the stone dust will provide a more stable base. Any opinions out there?

treebeard

03:05AM | 04/28/04
Member Since: 01/14/03
264 lifetime posts
Unless you're planning to move this deck about and use the 2x4's as skids, I think you'd be much better off forgetting the 2x4's, forget the stone or stone dust, and plan to support your deck on some form of corner and/or mid-span support, even if it's only concrete block buried in the ground on a well compacted base.


rwiens

05:24AM | 04/28/04
Member Since: 08/13/01
13 lifetime posts
I had considered a similar approach, whereby I would make 'strip' footings with concrete blocks or paving stones and then lay the joists on those. The deck will be 16'x16', so I figured three footings should do it. I thought the 2x4 approach (essentially the same thing but replacing the blocks/paving stones with wood) might be easier (less work). My biggest concern is where the wood has the potential to be in contact with water (i.e. sitting on an surface like concrete), which is why I suggested the crushed stone approach.

treebeard

08:00AM | 04/28/04
Member Since: 01/14/03
264 lifetime posts
Unless the stone mat that you're suggesting had permeable material beneath it, or a method of draining off the water that would collect in the stone, you'd really only be creating a bowl full of stone and water on top of which your structure would sit. The water would have to be evacuated somehow. If the existing soild beneath the stone is permeable free draining gravel, then the water would probably perc into the ground, no guarantees.

One other concern with your suggested plan might be the earth beneath the deck itself. If the soil heaves at all under the deck, so would the deck structure.

Good luck.

rwiens

12:12PM | 04/28/04
Member Since: 08/13/01
13 lifetime posts
I think this is what we are both talking about, although it was never my plan to get this fancy.

http://www.askthebuilder.com/187_Ground_Level_Deck_Construction_-_Grade_Beams_.shtml

Anonymous

08:34PM | 04/28/04
I've never heard of using grade beams until I read that ummm, bit of wild info... tells me he isn't a contractor at all, that guy asking was from IOWA too... he'd have to set piers down 4' in that area I believe?.. anyway got to take everything with a grain of salt. I've only been at it 30 years but man...

It's going to depend on your soil type, grade and location.

Listen to Treebeard, on the floating deck. Forget the 2x4's on grade... as he says use decking blocks... but location is a big factor in floating decks.

For a non-floating deck use ground treat 4x4 to your frost level set in concrete use the pt ends in the ground to flush beams, or if you have the room girders.. not steel like the article says :) have a look at my deck site http://decks.ca.com at the beam sizing page... not finished yet but it'll give you an idea on spans & loads etc.

Anything over 30" above grade do it properly with footings & piers and permits.

Altereagle

08:38PM | 04/28/04
Member Since: 12/27/02
543 lifetime posts
I've never heard of using grade beams until I read that ummm, bit of wild info... tells me he isn't a contractor at all, that guy asking was from IOWA too... he'd have to set piers down 4' in that area I believe?.. anyway got to take everything with a grain of salt. I've only been at it 30 years but man...

It's going to depend on your soil type, grade and location.

Listen to Treebeard, on the floating deck. Forget the 2x4's on grade... as he says use decking blocks... but location is a big factor in floating decks.

For a non-floating deck use ground treat 4x4 to your frost level set in concrete use the pt ends in the ground to flush beams, or if you have the room girders.. not steel like the article says :) have a look at my deck site http://decks-ca.com at the beam sizing page... not finished yet but it'll give you an idea on spans & loads etc.

Anything over 30" above grade do it properly with footings & piers and permits.

http://www.altereagle.com/

Alter Eagle Construction & Design

rwiens

07:08AM | 04/29/04
Member Since: 08/13/01
13 lifetime posts
...since the code in my area would require piers below the frost line (48") if it is attached to the house. My major design constraint is that the top of the deck can only be about 6" above the current grade (to align with a door threshold) So even if I used deck blocks, I would have to dig them into the ground a fair ways, and I would need to support each joist (16) in three places (16' long), for a total of 48 blocks! I thought it would just be easier to excavate the whole area, throw down some crushed stone for drainage and then put the joists on top.

Or am I missing something?
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