Timber vs aluminium base rails for commercial polytunnels

 

Say you're replacing a polytunnel cover. The timber around the doorway is showing signs of rot and crumbles between your fingers. This may be due to watering and muddy boots keeping the corners wet. Before fitting the new cover, there's another decision to make: replace the damaged rail with timber or switch to aluminium.

The cheaper wooden rail won't last as long for commercial polytunnels. An economical timber range brings the starting price down, but what happens after delivery? Aluminium needs different upkeep, and converting means paying for the connections and work needed to fit it. The key question is how much it will cost to replace the existing timber rails with aluminium.

What does the base rail do?

Along the tunnel, the base rail forms part of the structure holding the cover at ground level. How the polythene attaches depends on the system supplied.

The timber batten traps the polythene against the side or base rail. Undo it, and you start to see what releasing the sheet involves. Aluminium? You need the drawing: the specified profile and its matching fittings together explain how you'll attach the cover, tighten it and eventually take it off.

Both quotations for commercial polytunnels say what the rails are made of. Neither explains the joint at the hoop. That's a gap when you're ordering parts: you need a fixing drawing to see how they'll connect, and the photograph of an aluminium section may not be enough to progress.

Is timber cheaper than aluminium?

An economical timber range doesn't tell you the cost of changing this tunnel. Timber is offered as a lower-cost alternative in some commercial ranges, but conversion brings its own bill.

One quotation prices timber rails; the other prices aluminium. Before the totals mean anything, you need to find the battens, fixings and fitting labour on the timber quote, then the connections to the existing structure on the aluminium one. Anything missing still has to be supplied.

What is the difference in price? We can't give a figure without those quotations. Tunnel length, rail specification, delivery and fitting arrangements all affect the total.

For commercial polytunnels, compare the same scope of work:

•            Does each price cover the whole perimeter being replaced?

•            Are cover fixings and connections included?

•            Is taking out the old timber and installing its replacement part of the price?

•            Does either option alter the planned cover installation?

Doing the work yourself removes a labour charge. It also leaves you responsible for following the specified assembly and arranging help to handle the cover.

What changes in damp conditions?

Back beside the doorway, the soft patch needs investigating before another rail goes down. Is water collecting against it? Has soil built up around the timber?

The timber looks sound further along. What about around the fixings? Deterioration there matters. Aluminium does not rot like timber, but loose joints still need attention, and damaged connections may need replacing. Swap the rail beside that puddle and the water stays where it was.

Does changing the material solve wet ground around commercial polytunnels? No. Until the drainage problem is addressed, the replacement sits in the same wet working conditions.

There is no useful universal lifespan to attach to either option here. Timber specification, exposure and the way the rails are installed affect the comparison.

Will aluminium make re-covering easier?

When the old sheet comes off, what has to come apart?

Follow the grower's job through to the replacement sheet being tensioned. First, the old cover fixings come away. Which pieces survive for reuse? Which need replacing? A batten might come off cleanly, yet the job still stops if the timber underneath won't hold its fixings again.

An aluminium quotation has to answer those questions too. The profile alone doesn't explain the re-covering process.

Cover tension adjustment depends on the fixing system, not simply the rail material. Ask the supplier to confirm how the polytunnel cover is secured and tensioned, and whether the proposed system allows adjustment during re-covering.

Can aluminium replace the existing timber rails?

Only if the proposed arrangement suits the structure.

An aluminium box profile arrives, but its fittings don't meet the existing joints. Being sold for polytunnels hasn't made it suitable for this one. Before ordering, provide the supplier with the tunnel model, dimensions and clear photographs of the joints. This will help them check whether the aluminium profile and fittings are compatible with the existing structure.

Compatibility matters across commercial polytunnels because the rail, fittings and cover attachment have to work together. An apparently cheaper component loses its advantage if the remaining parts don't fit.

What should happen before ordering?

Check the complete structure and its anchoring for the site. A base rail doesn't replace correctly specified foundations or anchors.

Send the tunnel's measurements and connection photographs with one description of the replacement job, asking for an itemised price for each material. Before comparing totals, get written answers on fit, tension adjustment, and who does the installation.

Contact us to talk through the details of your base rail replacement.

Read More:

Commercial polytunnels: Is there a size limitation, and how do you choose?

How to choose the best commercial polytunnel covers: thickness, UV protection and light diffusion