The best Royal Victorian greenhouse foundation is a continuous concrete beam under all four walls. Janssens and Exaco recommend a strip at least 8" wide that goes down to your frost line. The published snow and wind ratings assume a beam at least 8" wide and 16" tall, with anchors set into it.
Gravel, pavers and other floors go inside that frame. This guide covers the foundation, the anchors and the floor, in the order you will build them.
✅ Quick answer
- Foundation: a continuous concrete beam or solid-grouted block wall, at least 8" x 16", under the whole perimeter.
- Anchors: every kit has corner anchors that reach 12" below ground. The VI36 and VI46 add a pair at the middle of each long wall.
- For the full ratings: a foundation connection at each vertical wall post, about every 750 mm (29.5").
- Flooring: not included. Gravel drains best. Pavers, brick, concrete or tile also work.
- Timing: set the anchors in concrete only after the frame is built, level and square.
Why does a Royal Victorian greenhouse need a real foundation?
A Royal Victorian is an aluminum frame filled with 4mm tempered glass. Glass is heavy, and it does not flex. If one corner sinks, panes bind and doors stick.
The kit comes with a low aluminum base frame, but not a foundation. The assembly manual says the greenhouse should sit on a solid concrete foundation deep enough to reach firm, frost-free ground. It also says anchoring is vital and should be checked from time to time.
There is a warranty reason, too. The manual states that damage from anchoring outside the manufacturer's recommendations is not covered.
📌 Have it ready first: the foundation must be level and square before delivery day. Pour it well ahead so the concrete has time to cure.
What foundation do the snow and wind ratings assume?
Exaco has an engineering letter for all four standard sizes. It is from Hollingsworth Pack, dated April 2020, under the 2015 International Building Code. Here are the ratings for each model.
| Model | Size (manual) | Ground snow | Wind (3-sec gust) | Price guide* |
|---|---|---|---|---|
| VI23 | 7'8" x 10'2" | 30 psf | 130 mph | ~$9,799 |
| VI34 | 10'2" x 15' | 25 psf | 120 mph | ~$11,399 |
| VI36 | 10'2" x 19'10" | 25 psf | 115 mph | ~$13,900 |
| VI46 | 12'7" x 19'10" | 25 psf | 115 mph | ~$16,400 |
*Prices checked in November 2026, all-glass version. Prices can change and sales may apply, so click the model name to see today's price.
Those numbers only hold when three conditions are met. The letter lists them:
- Foundation: a concrete beam or solid-grouted masonry wall at least 8" wide by 16" tall, continuous under the perimeter walls.
- Connections: a "PRO 210" type foundation connection at each vertical wall member, about 750 mm on center.
- Bracing: knee-brace scrolls at mid-bay on the VI23, VI34 and VI36, and at every bay on the VI46.
If your town asks for paperwork, structural letters and permit sets are available. The manual notes they are Texas-stamped, so ask your building office if that works for them. You can compare loads for your area with our snow and wind load calculator.
Which foundation type should you choose?
The manual says owners have used full slabs, concrete footers, pier and beam, and even timbers. They do not all perform the same. Here is how we explain the choices to our customers.
| Foundation | Meets rating spec? | Best for | Watch out for |
|---|---|---|---|
| Concrete strip beam | Yes, at 8" x 16" or larger | Most yards; gravel or soil floor inside | Must reach frost line; leave anchor holes |
| Masonry stem wall | Yes, if solid-grouted, 8" x 16" min. | Extra height and a classic look | Needs a drop door kit; more skill and cost |
| Full concrete slab | Ask an engineer about the edge | Garden rooms, wheelchairs, easy cleaning | Needs a floor drain or slope; no in-ground beds |
| Treated timber | No | Mild, sheltered sites only | Wood may wear out before the greenhouse |
"Meets rating spec" refers to the engineering letter's foundation conditions. Your local code and soil may call for more.
For most homeowners, the concrete strip beam is the sweet spot. It meets the spec, uses less concrete than a slab, and lets you choose any floor inside.
💡 Using wood? The manual says to put a barrier material between pressure-treated wood and the aluminum frame. Some treated lumber can react with bare aluminum over time.
Want to compare these options for other greenhouse brands too? Our practical guide to a greenhouse foundation covers every type in more depth.
How much concrete does a Royal Victorian foundation need?
A perimeter beam uses far less concrete than most people expect. You can estimate it in two minutes.
🧮 Formula: concrete for a perimeter beam
Perimeter (ft) = 2 x (width + length)
Cubic feet = perimeter x beam width (ft) x beam depth (ft)
Cubic yards = cubic feet ÷ 27. Add about 10% for waste.
Worked example: the VI36. The manual lists the VI36 at 10'2" x 19'10", or about 10.17 x 19.83 ft.
- Perimeter = 2 x (10.17 + 19.83) = 60 ft.
- An 8" x 16" beam is 0.67 ft x 1.33 ft.
- 60 x 0.67 x 1.33 = about 53 cubic feet.
- 53 ÷ 27 = about 2.0 cubic yards. With 10% extra, order about 2.2 cubic yards.
This is an estimate. If your frost line is deeper than 16", the beam gets deeper and the volume goes up. Try your own numbers in our greenhouse foundation calculator.
How do you build the foundation, step by step?
- Check permits. Call your building office before you order. Ask about size limits, setbacks and footing depth.
- Pick the site. Choose full sun and good drainage. The manual also says to choose a spot protected from strong winds.
- Get the exact base frame size. Use the foundation page in the assembly manual for your model. Do not build from the rounded "10x20" name.
- Plan pipes and wires. The manual suggests running water and power under the base frame. Lay the conduit before you pour.
- Dig and form the beam. Go at least 8" wide, and down to your frost line.
- Leave anchor holes. At each corner, leave a hole about 4" across. Leave matching holes for the VI36 or VI46 midpoint anchors.
- Pour, level and cure. A level top is everything. Measure both diagonals; they should match.
💡 Building on a stem wall? Our stem wall greenhouse guide walks through height, doors and drainage.
How do you anchor a Royal Victorian greenhouse?
Anchors stop wind from lifting or sliding the greenhouse. Every Royal Victorian kit includes corner brackets attached to the base frame. They extend an extra 12" below ground level.
The VI36 and VI46 include one more pair for the midpoint of the long walls. In very windy areas, or to meet permit specs, you can buy extra corner anchor posts (part PRO210) for the vertical members.
The manual gives two ways to fix them:
- Embed them in concrete. This is the method the manual describes first.
- Use them as L brackets. Trim the anchors at ground level, cut them into sections, and bolt them to the foundation with the right hardware.
⚠️ Don't rush the anchors: the manual says not to set anchors in concrete until the whole frame is complete, level and square. Set them too early and you lock in any mistake.
For the full ratings, plan a connection at each vertical wall post, plus the knee-brace scrolls. The Deco Scroll Reinforcement kit adds scrolls; call us and we will confirm what your model and site need. For drilling and bolting tips, read how to anchor a greenhouse to concrete.
What do you need for a stem wall or knee wall?
A low wall lifts the glass, adds headroom and gives a grand look. But the door frame sits on the base frame, so the doorway ends up high off the ground. The manual says a door extension kit is required.
- Drop door kit: our Royal Victorian drop door kit lowers the door 20" to 36". The glass above the doors is not included and is ordered locally.
- Hinged doors: if your greenhouse comes with sliding doors and goes on a stem wall, upgrade to hinged doors for easy access.
- One kit for doubles: a double hinged door needs only one drop door kit.
What is the best flooring for a Royal Victorian greenhouse?
The greenhouse does not include flooring, so you can match the floor to how you will use it. The manual lists soil, gravel, pavers and bricks, wood, a concrete slab and tile.
| Floor | Drainage | Feel and look | Good for |
|---|---|---|---|
| Gravel | Excellent, drains naturally | Natural, low cost | Growers who water a lot |
| Pavers or brick | Good, through the joints | Firm, classic | Paths, benches, carts |
| Soil beds | Good | Can get muddy | In-ground crops like tomatoes |
| Concrete slab | Needs slope or a drain | Clean, easy to sweep | Garden rooms, pots only |
| Tile | Plan for runoff | Elegant, slippery when wet | Sunrooms and seating |
Drainage and tile notes follow the Royal Victorian assembly manual.
Many of our customers mix floors. They lay pavers down the center path and keep gravel or soil under the benches. That gives you a firm walkway and good drainage where you water.
🧮 Quick gravel estimate (VI36)
Floor area ≈ 10.17 x 19.83 = about 202 sq ft. At 3" deep (0.25 ft): 202 x 0.25 = about 50 cubic feet. 50 ÷ 27 = about 1.9 cubic yards of gravel, before any pavers.
What mistakes should you avoid?
- Building from the nickname size. A "10x20" VI36 is really 10'2" x 19'10". Use the manual's foundation page.
- A beam that is not level. Glass panes and sliding doors need a flat base.
- Setting anchors too soon. Wait until the frame is square.
- Forgetting the doorway on a stem wall. Order the drop door kit with the greenhouse.
- Leaving snow on the roof. The manual says to clear snow, and the warranty does not cover damage from snow buildup.
What will the whole project cost?
The kit is the biggest line, but plan for the rest too:
- The greenhouse: see the table above for the price guide. Shipping is free to the continental US.
- Foundation: concrete, forms and labor. Get local quotes, since prices vary a lot by region.
- Floor: gravel is the cheapest; pavers and tile cost more.
- Extras: a drop door kit or hinged doors for a stem wall, and scroll reinforcement if needed.
- Assembly: do it yourself, or hire a crew from our Assembly Crews page.
📌 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 (November 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.
Still choosing a size? Our Royal Victorian VI46 review and the full Victorian greenhouse collection can help.
Frequently asked questions
Does a Royal Victorian greenhouse come with a foundation?
No. It comes with an aluminum base frame and corner anchors, but you build the foundation. Plan a concrete beam or solid-grouted block wall, at least 8" x 16", under the perimeter.
Can I put a Royal Victorian greenhouse on pavers or gravel?
Yes, as the floor inside. The frame itself should still sit on a solid, frost-free concrete foundation. The snow and wind ratings assume that kind of base.
How deep should the foundation be?
The manufacturer recommends an 8" wide strip that goes down to the frost line in your area. The engineering letter calls for a beam at least 16" tall. Your local code may require more.
Can I use a wood foundation?
Some owners do, in mild and sheltered sites. Use pressure-treated wood with a barrier between it and the aluminum. A wood base does not meet the rating spec and may wear out before the greenhouse.
Do I need a permit?
It depends on your town and the greenhouse size. Many towns require one for the larger models. Structural letters and permit sets are available, so call us before you apply.
When do I set the anchors in concrete?
Last. Build the frame first, then check that it is level and square. Only then fill the anchor holes with concrete.
Planning your Royal Victorian foundation?
We are a small, woman-owned business in Georgia, and we answer every question personally. Send us your model, your yard and your climate. We will help you plan the foundation, doors and anchors, line up an assembly crew, and confirm today's price with free shipping.
