Wood vs. Aluminum Greenhouse: Which Framing Material Is Better?

When choosing a greenhouse, most naturally focus on size, style, glazing, ventilation and price. But one of the most important decisions is the material used to build the greenhouse frame.

For permanent residential greenhouses, the two most common choices are wood and aluminum. Both materials can make an attractive and functional greenhouse, but they perform differently when it comes to insulation, growing, strength, longevity, ease of modification, heating and cooling, repairability, and sustainability.

Here is how wood and aluminum greenhouse framing compare.

Insulation: Wood Framing Has a Natural Advantage

One of the biggest differences between wood and aluminum is thermal conductivity.

Wood is naturally insulating. Depending on species and density, softwoods commonly have an R-value of roughly R-1 to R-1.4 per inch. Aluminum, by comparison, is an excellent conductor of heat and provides essentially no meaningful (effectively near R-0) insulating value by itself.

That matters in a greenhouse because the frame combines with the otherwise insulated or semi-insulated glazing system.

During cold weather, an aluminum frame transfers heat from the warm greenhouse interior to the colder exterior. This is known as thermal bridging. High-quality aluminum greenhouse manufacturers can reduce this problem with added complexity and cost.

Wood framing does not require a thermal bridge because the material itself is a relatively poor conductor of heat with a higher R-value.

It is important to keep this difference in perspective. Most greenhouse heat loss occurs through the large areas of glass or polycarbonate rather than through the frame. Nevertheless, reducing thermal bridging at hundreds of feet of framing can contribute to a more thermally efficient structure.

Heating Costs: An Advantage for Wood Framing

Because wood transfers heat much more slowly than aluminum, a wood-framed greenhouse has less heat loss through its structural members.

That can mean lower heating requirements, particularly in cold climates and in greenhouses that are heated throughout the winter.

The actual savings will depend on many factors, including:

Greenhouse size Amount and type of glazing Outside temperature and wind Desired inside temperature Air leakage

Insulation options Foundation and basewall construction Heating equipment

For someone planning to maintain a greenhouse at 45°F, 50°F or even 60°F during a cold winter, every improvement in the building envelope helps.

What About Cooling?

The framing material itself generally isn't a primary driver of cooling requirements. 

A greenhouse's summer temperature is primarily influenced by solar gain through the glazing, along with ventilation, shading, outside temperature and air movement.

Whether your greenhouse is wood or aluminum framed, good summer temperature management typically requires some combination of roof vents, lower intake vents, exhaust fans, circulation fans and shade cloth.

Wood's lower thermal conductivity reduces heat transfer through the frame, but effective greenhouse cooling is primarily a matter of controlling sunlight and moving air.

Strength: Both Can Be Strong—But in Different Ways

Both wood and aluminum frames can produce very strong greenhouses when they are properly engineered.

Aluminum has an excellent strength-to-weight ratio, allowing manufacturers to create relatively narrow structural members. Engineered aluminum extrusions can also incorporate channels for glazing, seals, and fasteners.

Wood uses larger structural members that can create an exceptionally strong and rigid greenhouse. However, not all wood species have the same structural properties. Redwood's strength allows a well-designed greenhouse to use relatively narrow structural members compared with many cedar greenhouse designs. Larger cedar structural members block more sunlight and cast wider shadows across the plants and growing areas. Redwood therefore offers an attractive balance of structural strength, durability, and slender framing that helps maximize the light entering the greenhouse.

A wood rafter, beam or post has both strength and mass. Wood framing can also be reinforced relatively easily with gussets, rafter ties, beams, posts, cables and additional structural members when higher snow or wind loads need to be accommodated.

The important comparison isn't simply wood versus aluminum.

It is the engineering of the complete greenhouse.

A lightweight greenhouse made from either material should not be assumed to have the same structural capacity as a greenhouse specifically engineered for heavy snow or high winds.

Longevity: A Well-Built Greenhouse Should Last for Decades

Aluminum framing has an obvious advantage in that it does not rot. Quality aluminum framing with an appropriate finish can provide decades of service.  That doesn't mean wood is inherently short-lived.

The species of wood makes an enormous difference.

Redwood and other naturally durable species have long histories of use in outdoor structures because they resist decay significantly better than many common construction woods.

Good design matters too. Keeping wood away from standing water, providing proper drainage, maintaining exterior finishes when appropriate, and using suitable fasteners all contribute to longevity.

A properly designed and maintained premium wood greenhouse should be viewed as a long-term structure, not a temporary garden accessory.

Painted Wood Can Look Surprisingly Similar to Aluminum

Some homeowners assume a wood greenhouse must have a natural brown or stained appearance.

It doesn't.

Wood can be stained to emphasize its grain, but it can also be stained or painted with a quality solid exterior finish. White, black, gray, green and other colors can dramatically change the appearance of a wood greenhouse.

With a smooth solid-color finish, particularly when viewed from outside through the glazing, many people may not immediately recognize whether the greenhouse framing is wood or another material.

That gives homeowners an interesting choice.

You can celebrate the warmth and natural appearance of wood—or use a solid finish to create a more contemporary architectural appearance while retaining the functional advantages of wood framing.

Repairs: Wood Framing Is Remarkably Forgiving

One of wood's most practical advantages becomes apparent years after the greenhouse is installed.

Wood is easy to repair.

If a wood component is damaged, one can often repair, reinforce, splice, or replace the affected piece using ordinary household tools and readily available fasteners.

A damaged aluminum extrusion can be more challenging. The original profile may be proprietary to the greenhouse manufacturer, and a replacement component may have to come from that manufacturer.

If the greenhouse is 25 or 40 years old, will that exact aluminum extrusion still be available?

With wood, a skilled carpenter can often fabricate what is needed.

That repairability can be an important part of the true lifetime value of a greenhouse.

Wood Is Easier to Modify

Gardeners rarely leave their greenhouses exactly as they were on the day they were installed.

You might eventually want to add:

Shelves Benches Fans Grow lights Irrigation lines Thermostats Shelves Benches Fans

Grow lights Irrigation lines Thermostats Electrical conduit Sensors Plant supports Lights for People Tool walls Hanging baskets

Wood makes those modifications easy.

A screw can often be driven directly into a wood rafter, stud, beam, or post at the location where it is needed.

With aluminum framing, attachments often require specialized clips, channels, brackets, bolts, or fasteners compatible with the manufacturer's extrusion system.

That isn't necessarily difficult, but wood offers a wonderful advantage to the gardener who likes to say:  "I want a hook right here."

With wood, that is usually a very simple request.

Hanging Plants and Lights

This seemingly small issue becomes surprisingly important once you begin using a greenhouse.

Hanging baskets are heavy—especially immediately after watering. Grow lights, circulation fans, irrigation lines, and plant supports also need secure attachment points.

Substantial wood rafters and beams provide convenient locations for appropriately sized hooks and fasteners.

This flexibility allows the greenhouse interior to evolve with the gardener.

Today you may be growing tomatoes.

Five years from now, you may have orchids hanging from the rafters, citrus trees along the wall, seedling lights above a propagation bench, or climbing vines supported overhead.

A greenhouse should accommodate those changes.

Sustainability: Wood and Aluminum Have Very Different Origins

The environmental comparison between wood and aluminum is complicated, and both materials have advantages and impacts.

Aluminum begins with bauxite ore, which must be strip mined from the earth. The ore is refined into alumina and then converted into aluminum through an energy-intensive smelting process. Mining and refining can result in land disturbance and other environmental impacts.

Aluminum's major environmental advantage is at the other end of its life cycle: it is highly recyclable. Recycling existing aluminum requires far less energy than producing primary aluminum from newly mined bauxite.

Wood follows a very different cycle.

Trees are a renewable biological resource. When forests are responsibly and regeneratively managed, trees can be harvested and replaced by new growth. Growing trees also absorb carbon dioxide from the atmosphere and store carbon in their wood.

That means the sustainability question isn't simply: Wood or aluminum?

Better questions are:  Where did the material come from? How was it produced? How long will it last? Can it be repaired? And what happens to it at the end of its useful life?

Responsibly sourced, durable wood used in a greenhouse that lasts for decades can be an excellent environmental choice.

Likewise, an aluminum greenhouse made with significant recycled content and ultimately recycled again can have a much different environmental footprint than one made primarily from newly produced aluminum.

The Importance of Choosing the Right Wood

Not every wood is equally suited to greenhouse construction.

Greenhouses are unusually demanding environments. They combine moisture, condensation, irrigation, soil, fertilizers, temperature changes, and year-round exposure to the weather.

That makes naturally decay-resistant species particularly valuable.

Redwood is exceptionally well suited to greenhouse construction because of its natural durability, dimensional stability, workability, beauty, and relatively low thermal conductivity.

Higher grades of redwood—particularly heartwood—provide substantially greater natural resistance to decay than ordinary construction lumber.

That is one reason redwood has historically been used for outdoor applications ranging from decks and siding to garden structures and greenhouses.

Wood vs. Aluminum Greenhouse Framing: Quick Comparison

Consideration	Wood Greenhouse	Aluminum Greenhouse
Natural insulation	Excellent	Very low unless thermally broken
Thermal bridging of Frame	Low	High without thermal breaks
Structural strength	Excellent when properly designed	Excellent when properly engineered
Longevity	Decades with appropriate species/design	Decades with quality aluminum
Rot resistance	Depends strongly on wood species	Does not rot
Corrosion	Not applicable to framing	Finishes can offer corrosion resistance
Repairability	Excellent	Can depend on replacement extrusions
Ease of modification	Excellent	Often requires compatible hardware
Attaching lights in or outside	Simple	May require specialized clips or brackets
Hanging plants	Simple with proper fasteners	Often uses extrusion-specific hardware
Heating efficiency	Thermal advantage	Thermal bridging can increase heat transfer
Summer cooling	Primarily determined by glazing, shade and ventilation	Primarily determined by glazing, shade and ventilation
Appearance	Natural or solid-color finish, or clean, contemporary appearance	Clean, contemporary appearance
Renewable raw material	Yes, when responsibly sourced	No
Sustainability	Renewable, stores carbon while in use, repairable, relatively low processing requirements	Highly recyclable, but primary aluminum requires mining and energy-intensive refining and smelting
Recyclability	Reusable/biodegradable depending on finish and treatment	Excellent
Manufacturing	Less energy intensive	Primary aluminum production is highly energy intensive

 

Foundation: Both Wood and Aluminum Greenhouses Need One

Regardless of whether a greenhouse is framed with wood or aluminum, a permanent greenhouse needs to be securely attached to a good foundation.

The foundation provides a level, stable base for the greenhouse and, just as importantly, anchors the structure against wind. A greenhouse has a large surface area, and wind pushing against the walls and roof can create significant uplift and lateral forces.

Simply setting a lightweight aluminum greenhouse on the ground without adequate anchoring can make it a gift to your neighbor when the next windstorm arrives.

Wood greenhouses aren't exempt from this requirement. Although a substantial wood greenhouse may be considerably heavier, weight alone should not be relied upon to hold a greenhouse in place.

Foundation choices can include treated-timber foundations, concrete piers, concrete slabs, concrete or masonry stem walls, and other properly designed systems. The appropriate foundation depends on greenhouse size, local soil conditions, frost depth, wind and snow loads, and local building requirements.

The important principle is the same for either framing material: the greenhouse and its foundation should work together as one structure. A strong greenhouse is only as secure as the foundation to which it is anchored.

So, Which Is Better: Wood or Aluminum Framing?

There is no single greenhouse framing material that is best for every application.

Aluminum is lightweight, durable, corrosion resistant and capable of creating greenhouses with narrow framing members. Its recyclability is also a significant advantage.

But for a homeowner looking for a permanent garden structure, wood offers some compelling benefits.

Wood-framing naturally insulates. It is strong. It is easy to repair and modify. It provides convenient attachment points for everything from hanging baskets to grow lights. It can be finished naturally or painted to complement almost any architectural style. And when durable wood comes from responsibly managed forests, it is a renewable building material.

Perhaps most importantly, a wood greenhouse can adapt.

Gardens change. Gardeners change. The plants you grow today probably won't be exactly the plants you grow ten years from now.

A greenhouse should be able to change with you.

That is one of the quiet advantages of building a greenhouse from wood: it isn't just a frame around your plants. It is a structure you can work with for decades.

Why Sturdi Built Uses Redwood

Sturdi Built Greenhouse has been building wood greenhouses since 1952. We use clear, all-heart redwood because a greenhouse isn't an ordinary outdoor building.

Redwood is framing material that is naturally durable, structurally substantial, beautiful, workable and well suited to the unique environment inside a greenhouse.

If you want a greenhouse that combines the warmth of natural wood, excellent repairability, flexibility, strength and timeless garden architecture, a well-built redwood greenhouse deserves a very close look.