You want a low ground level deck with the smallest step possible off the ground using standard material. Well, decking needs joists to support it, and the lowest joists are 2×4’s. Can you use 2×4’s for a ground-level deck?
A ground-level deck can be built from 2×4 if the span is less than 5’8″ (1.72m), using ground contact treated lumber. Under a 2×4 deck, the ground will need to be covered to prevent weed growth through the decking on such a low deck. The decking needs to be designed for ground contact or sufficiently raised off the ground to prevent rot.
Well then, that is simple enough. Short spans, ground cover, and decking that will last close to the ground. It provides a simple platform, getting your feet and chairs out of the mud, increasing enjoyment in your yard.
Let’s get to it. Explain these few but essential requirements.
2×4 Deck Joist Can Only Span 5’8″ (1.72m) Between Supports.
Either you are limited to a small deck, less than 6′ (1.8m), or you will need a mid-span beam. You can sneak out a few more inches if you set the 2×4’s at 12″ (300mm) on centre, but commonly deck joists are 16″ (400mm) o.c.
Yes, a ground-level deck rarely requires a permit, meaning you can use any material you want. But you still want the deck to last, so build to code as much as possible.
A deck 6′ (1.8m) deep is not practically of much value. Unless you and your buddies just want to set up a row of deck chairs and soak up the sun. A larger deck has much more value, both with the potential of setting up a table or a semi-circle more conducive to conversation.
An easy solution for a bigger deck with 2×4 joist, is support the joists on a 6×6 post buried in the ground. Three 6×6 posts, one on each end plus at mid-span, allow you to use 2×4 joists but is still strong enough to not flex with every step.
If you don’t want to use and dig in a 6×6 post, another option is to build two 2×4 sections with joists 66″ (1676mm) long and double up the rims on one end and then nail or screw together the two sections on the single 2×4 side. Creating a flush beam providing a little extra strength for the 2×4’s. Combining the two sections giving you a full 12′ (3.6m) deck. You will need to support the 2×4 flush beam off buried deck blocks. Providing the support, they need without additional height or digging.
A third option is to substitute 4×4 fence posts for the 2×4. The advantage is they are more robust, can rest directly on the ground and require minimal support. The wider width of the post will minimize deflection while providing a good base to block. Providing support from the ground to the deck substructure.
2×4 Deck Joists Need to Be Treated for Ground Contact
Whatever design you use, any lumber within 6″ (150mm) of the ground needs to be treated for ground contact or your going to be rebuilding that deck is in the next few years.
4×4 fence posts, of course, are treated for ground contact, designed to be buried.
If using 2×4’s shop around for incised wood stamped for ground contact. Not as common as appearance grade lumber treated lumber. As they are more expensive and don’t look as good. But if you are building on the ground, it is a must.
Ground Cover Under a 2×4 Deck
There are two reasons for ground cover under a 2×4 deck.
The first is weeds. Being so low to the ground, weed seeds will easily sprout and grow up between the decking. Making your beautiful deck look more like a weed patch than a platform for sunning. Pulling the weeds off as they sprout through the decking will be an endless task, with weeds sprouting up as fast as you pick them.
A better solution is landscape fabric with a couple of inches of gravel on top. The landscape fabric will prevent weeds from growing through the decking. The gravel keeping the landscape fabric in place while providing a base for the 2×4’s. Both supporting the joist while draining away water. Which will minimize joist rot and frost heave.
2×4 decks are much more common over concrete slabs. Which is even better to reduce weeds. But the joist should be slightly raised with shims above the concrete. Both for levelling the deck and provide room for water to run off the concrete. For it doesn’t pool and rots the 2x4s. The gap between the 2×4 and concrete will also allow air circulation, which is important for the decking.
2×4 Deck Joist will Limit Decking Options
Like the 2×4’s, decking so close to the ground needs to be designed for ground contact or steps taken to protect the decking.
Composite decking like Moisture Shield. One of the few deckings is designed for ground and water contact. It is something else.
Timbertech decking with its full polymer cap is also an option, allowing installation with as little as 1 ½” (38mm) clearance from the ground. A 2×4 resting on the ground provides twice that clearance.
Composite decking without a polymer bottom cap should not be used on 2×4 joists on the ground. Unless other steps have been taken to minimize ground contact.
Most wood decking is not designed for ground contact and should not be used on 2×4 joist within 6″ (150mm) from the ground. The exception is if you have sufficient drainage.
“Minimum ground clearance required 50mm over concrete, 150mm over dirt. Drainage and airflow beneath the deck is also very important to ensure a good looking long term deck.”Trex
Same as with composite decking not designed for ground contact can be done for wood decking. By laying a bed of gravel, a minimum of 3″ (75mm) over landscape fabric will sufficiently raise the decking off the ground as to prevent rot. Don’t forget to include a gravel perimeter bed around the decking edge to prevent the border of the decking from rotting.
2×4 Deck Joists Need Additional Ventilation
Ventilation for a low deck can be achieved in one of two ways.
Either with vent holes drilled in the rim on each side of the deck. With two holes for each joist cavity, one on each end. To allow for a cross breeze to dry out the 2×4 and the underside of the decking.
Decking can also be vented by increasing gapping between deck boards. A good decking gap is 3/8″ (10 mm) between decking boards. This is sufficient both for composite and wood decking. To allow moisture to evaporate through the deck boards preventing water from being trapped under the deck.
Deck’s with 2×4 Joists Cannot Support Railing
For a ground-level deck, this should not be a problem but something to be aware of. The Canadian Wood Council wood deck chart requires a deck with guard railing to have a minimum of 2×8 joists. A ground-level deck does not require a railing. Therefore, they are mainly decorative, but lack of strength to attach to will limit the railing rigidity.
A 12’x12′ Ground Level Deck with 2×4 Joist Material List
- 2×4-12 Ground contact (12)
- 6×6-12 post ground contact (3)
- 5.5″ by 12′ Decking boards (25) gapped 3/8″ (10mm)
- Decking screws (500)
- Galvanized 3″ Ardox framing nails or 3″ treated screws for joists (100)
- Gravel 1.5 cubic yards
- Landscape fabric 200 sqft
Approximate cost for 2×4 deck substructure $600 for the substructure plus $400 for 5/4″ x5.5″ wood decking. Upgrading the 2×4’s to 2×8 to increase strength and raise the deck a little more out of the dirt will increase cost by about $300 to $900 for the substructure. Deleting the 6×6 post and using 4×4 ground contact post instead of 2×4 lowering the substructure cost to under $500 for material.
In Conclusion of A 2×4 Ground Level Deck
A ground-level deck can be framed out of 2×4 treated for ground contact. Ideally, sitting on top of a gravel bed providing strength and drainage while minimizing weeds. The only other limitations ar the decking proximity with the ground and lack of railing support. All of these challenges can be overcome with a good design and construction practices.
Allowing you to enjoy a deck low to the ground at minimal cost. Enjoy relaxing in your yard out of the mud and dust.