Building a greenhouse on a stem wall means setting the greenhouse on a low wall of concrete, block or brick instead of right on the ground. The wall lifts the frame above wet soil, adds headroom and gives the greenhouse a solid, permanent look. You don't always need one, but it is a great choice for heavy glass houses, sloped yards and anyone who wants extra height.
We are a small, woman-owned greenhouse business in Georgia, and stem walls come up in our phone calls every week. This guide covers what we tell our customers: when a wall makes sense, how tall to build it, how to fix the greenhouse on top and what to do about the door.
✅ Quick answer
- A stem wall (also called a knee wall or dwarf wall) is a low perimeter wall on a footing. The greenhouse bolts to its top.
- Most garden stem walls are about 1 to 3 feet tall. Taller walls add headroom but block low light.
- The footing should sit on firm soil and, in cold areas, below the frost line.
- The top must be flat, level and square to within the maker's tolerance.
- Raising the greenhouse raises the door sill. Royal Victorian owners usually need a drop door kit and hinged doors.
What is a stem wall for a greenhouse?
A stem wall is the short wall that "stems" up from a buried footing. The footing spreads the weight into the soil. The wall carries the greenhouse frame up above the ground.
Inside the wall, the floor can stay soil, gravel or pavers. That is different from a full concrete slab, which covers the whole floor. Many growers like this mix: a strong edge for the frame and an open floor for beds and drainage.
- Footing: a strip of concrete in a trench, wider than the wall.
- Wall: poured concrete, concrete block, brick or stone, from ground level up to the height you want.
- Top: a flat, sealed surface, often with a treated timber or metal plate, where the greenhouse base frame is fixed.
📝 A quick correction: not every greenhouse needs a stem wall. Many kits do very well on a timber frame, a maker's base frame or a slab. A stem wall is one good option among several. Our practical guide to a greenhouse foundation compares them all.
Why build a greenhouse on a stem wall?
Gardeners have set glass houses on low walls for well over a century. The reasons still hold up today.
- More headroom. Every inch of wall adds an inch of height inside. Tall crops and tall people both notice.
- Keeps the frame dry. The frame sits above splashing rain, snow and wet soil.
- Works on slopes. You can step the wall to make a level top on uneven ground.
- Holds heat. Masonry soaks up warmth by day and gives some back at night.
- Protects low glass. A wall takes the hits from mowers, trimmers and kicked balls.
- Looks permanent. A brick or stone wall can match your house and makes the greenhouse feel like part of the home.
What are the downsides of a stem wall?
A stem wall is not the right fit for every yard. Be honest with yourself about these points before you start.
- Cost and skill. It is masonry work. Most people hire a local mason or concrete contractor.
- Less low light. Solid walls shade the bottom of the greenhouse. Plan benches at or above wall height.
- Door changes. The door ends up higher off the ground. Some models need a kit to fix that.
- Tight tolerances. If the top is out of level or square, the greenhouse won't go together well.
- Hard to move. It is permanent. Check permits and property lines first.
Stem wall vs. slab vs. timber: which base should I choose?
Here is how a stem wall compares with the other common greenhouse bases.
| Base | Adds height? | Floor inside | DIY-friendly? | Best for |
|---|---|---|---|---|
| Stem wall on a footing | Yes, 1 to 3 ft typical | Soil, gravel or pavers | Some skill | Glass houses, slopes, a classic look |
| Concrete slab | A few inches | Concrete (needs drains) | Hire a pro | Easy cleaning, attached greenhouses |
| Concrete piers | Optional | Soil or gravel | Some skill | Sloped or frosty sites |
| Timber frame on gravel | A little, if stacked | Gravel | Yes | Small to mid-size kits |
| Maker's base frame | A few inches | Your choice | Yes | Riga and other matched kits |
For a glass greenhouse, a solid perimeter matters most. For example, the engineering letter for the Royal Victorian VI46 bases its snow and wind ratings on a continuous concrete beam or solid-grouted block wall at least 8 inches wide and 16 inches tall, with an anchor at each wall post. A stem wall fits that bill nicely.
How tall should a greenhouse stem wall be?
There is no single right height. Most garden walls we see fall between about 12 and 36 inches. Think about how you will use the space.
- 8 to 16 inches: lifts the frame out of splash and snow, with little loss of light. Good for in-ground beds.
- About 24 inches: the classic "dwarf wall" height. It lines up with bench height, so you lose little growing light.
- 30 to 36 inches: a grand look and lots of headroom, but the lowest part of the greenhouse gets no direct sun.
💡 Our tip: match the wall to your bench height. If your benches will be about 30 inches high, a 24 to 30 inch wall hides under them and costs you almost no usable light.
Also check your kit's door height. A taller wall means a taller step up, which brings us to the door question below.
How deep and wide should the footing be?
The footing is what keeps the wall from sinking or heaving. Its size depends on your soil, your climate and the weight of the greenhouse. That is why we always say: ask a local builder or your building department.
- Depth: in cold climates, the bottom of the footing should be below the local frost line. That can be 30 to 60 inches or more in the north. In much of the South it is far shallower.
- Width: a common starting point is a footing about twice as wide as the wall. Your contractor may size it differently for your soil.
- Soil: build on firm, undisturbed soil, never on loose fill or topsoil.
- Wind and flood zones: high-wind areas may need more anchoring. In a flood zone, local rules may set how high the structure must sit.
How do you build a stem wall for a greenhouse?
Here are the basic steps. A mason or contractor will follow a similar path, so this list also helps you talk to them.
- Get the exact base size. Use the outside base dimensions from your greenhouse manual, not the "nominal" size. Wait until you have them before you dig.
- Check permits and call 811. Ask about setbacks and frost depth. 811 marks buried lines for free.
- Lay out and dig. Mark the outline with stakes and string. Check that both diagonals match.
- Pour the footing. Add rebar if your contractor or code calls for it. Let it cure.
- Build the wall. Pour it in forms, or lay block or brick. Grout solid if the design calls for it.
- Set anchors. Place anchor bolts or plan anchor holes where the manual shows the frame fixings.
- Make the top perfect. Level it, check square again and seal it.
- Plan drainage and services. Leave weep holes or a drain path, plus sleeves for water and power.
⚠️ Don't build from the brochure: base sizes differ from the size in a product name. A "10x15" greenhouse may measure 10'2" by 15'. Build to the manual, and call us if any number is unclear.
How much block and concrete will I need?
You can rough out your materials with two simple formulas. They help you check a contractor's quote, too.
📐 Stem wall formulas
Blocks = (Perimeter in ft ÷ 1.33) × number of courses
Footing cubic yards = Perimeter × Width × Depth (ft) ÷ 27
Standard 8x8x16 block: each course is 8 in tall, each block 16 in (1.33 ft) long · Add 5–10% extra
🧮 Worked example: a 24-inch wall for a Royal Victorian VI34
- The Royal Victorian VI34 is about 10'2" by 15'. Perimeter = 2 × (10.17 + 15) = about 50.3 feet.
- A 24-inch wall is 3 courses of 8-inch block.
- Blocks: 50.3 ÷ 1.33 = about 38 per course × 3 = 114. Add 5% = about 120 blocks.
- Footing 16 in wide (1.33 ft) by 8 in deep (0.67 ft): 50.3 × 1.33 × 0.67 ÷ 27 = 1.66. Add 10% = about 1.8 cubic yards.
This is an estimate only. Your footing may need to be deeper or wider for frost and soil. Use the manual's exact base size and your builder's footing design.
How do I attach a greenhouse to a stem wall?
The greenhouse base frame must be fixed firmly to the top of the wall. Wind tries to lift a greenhouse, so this connection matters as much as the wall itself.
- Concrete or grouted block: use anchor bolts set in the wet concrete, or drilled anchors after it cures, at the spacing in your manual.
- Brick: finish with a solid top course (no holes on top) so screws and anchors have something to grip.
- Timber top plate: some builders bolt a treated plate to the wall and cover it with metal flashing. This gives a smooth, even surface. Seal any gaps against pests and drafts.
Brick and block walls can settle and crack over time. Check yours each spring, and fill small cracks with exterior sealant. Our step-by-step guide on how to anchor a greenhouse to concrete walks through the hardware.
Will I need a drop door kit?
Often, yes. When the greenhouse sits on a wall, its door sill sits on the wall too. On a 24-inch wall, that is a 24-inch step. A drop door kit lowers the door opening down toward the ground so you can walk straight in.
For Janssens Royal Victorian greenhouses, here is what the maker's details say:
- The Royal Victorian Drop Door Kit lets you drop the door by 20 to 36 inches. About 24 inches often works best.
- If your greenhouse comes with sliding doors and you want a stem wall, you must upgrade to hinged doors.
- A double hinged door needs only one drop door kit.
- The kit does not include the new glass panels needed above the doors. Those are ordered locally, and we may be able to supply polycarbonate panels you cut to size.
The kit comes in dark green or black to match your frame. The Cross Country Legacy 8x8 can also sit on a stem or knee wall with its drop door option, so ask us about it when you order. For other brands, call us before you build. Not every greenhouse is designed to sit on a raised wall. Learn more in our guide to greenhouse door kits.
Does a stem wall help keep a greenhouse warm?
It can help. A solid wall loses far less heat than glass or polycarbonate. Extension research from UMass found that insulating the low sidewalls of greenhouses often pays for itself in under two years.
- Insulate the inside face with rigid foam board below bench height.
- Insulate the outside below ground to keep the soil inside warmer. Ask your builder before backfilling.
- Use the mass. Dark masonry in the sun soaks up warmth during the day.
For more ideas, see our guide on how to heat a greenhouse without electricity.
How much does a greenhouse stem wall cost?
Masonry prices vary a lot by region, wall height and how much you do yourself. The best way to know is to get two or three local quotes. Plan for these items:
- Digging and footing concrete
- Block, brick or poured wall, plus grout and rebar if needed
- Anchors, top plate, flashing and sealant
- Permit fees, if your town requires one
- Door changes for your greenhouse model
For the greenhouse side of the job, here are approximate prices for the Royal Victorian parts we sell:
| Product | What it does | Approx. price* |
|---|---|---|
| Royal Victorian Drop Door Kit | Lowers the door 20–36 in | About $200 (hinged) / $299 (sliding) |
| Royal Victorian Hinged Door | Replaces sliding doors | About $1,399 single / $2,549 double |
| Royal Victorian VI34 | 10x15 glass greenhouse | About $11,499 (glass) |
*Prices checked in October 2026. Prices can change and sales may apply, so click the model name to see today's price.
📌 About prices: manufacturers update their prices during the year, and we often run sales and promotions. The price on the product page is always the current one. Prices in this article are a guide from when we wrote it (October 2026), not a quote or guarantee. Found a lower price for the same model at an authorized retailer? We offer a Price Match Guarantee - please check the rules first. Call us and we will confirm today's price and any current deals.
How can Mulberry Greenhouses help?
We answer every question personally. Send us your greenhouse model, a photo of your spot and the wall height you have in mind. We will check the base size, the door options and what to order together.
- Every greenhouse we sell ships free to the continental US.
- We can connect you with independent assembly crews once your wall is ready.
- Browse our Victorian greenhouse collection for models that pair well with a stem wall.
Planning a Royal Victorian? Our Royal Victorian foundation, anchoring and flooring guide covers that model in detail.
Frequently asked questions
Do all greenhouses need a stem wall?
No. Many greenhouses sit on a timber frame, a maker's base frame, piers or a slab. A stem wall is a strong choice for heavy glass houses, slopes and extra height, but it is optional.
How tall should a greenhouse knee wall be?
Most are about 12 to 36 inches. Around 24 inches is a popular height because it sits under bench level. Taller walls add headroom but shade the lowest part of the greenhouse.
How deep should a stem wall footing be?
It should rest on firm soil and, in cold areas, below the local frost line. Frost depth ranges from a few inches in the Deep South to 60 inches or more up north. Your building department can tell you the number.
Can I put a Royal Victorian greenhouse on a stem wall?
Yes. Use the Royal Victorian Drop Door Kit so you can walk in easily. If your model has sliding doors, the maker calls for upgrading to hinged doors.
Is block or poured concrete better for a stem wall?
Both work well when built right. Poured concrete is fast and very strong. Block is easier to do in stages and can be grouted solid. Brick or stone facing can be added for looks.
Do I need a permit for a greenhouse stem wall?
Often, because it is a permanent foundation. Rules vary by town and HOA, so check before you dig. Our greenhouse permit guide lists what to ask.
Planning a greenhouse on a stem wall?
We are a small, woman-owned business in Georgia, and we answer every question personally. Tell us your model and wall height, and we will help you plan the base, the door kit and your assembly crew.