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  • Writer's pictureKPM Partners

Should a silage clamp have a roof?

We all know the answer to the question “should your silage clamp have a roof” is - only if its raining! Whilst the motor industry has been developing cars with convertible roof for over 100 years, the guys working in agricultural building development have yet to perfect even a prototype convertible silage clamp. So if you're going to be stuck with either a fibre cement roof or a clear view of the heavens - which one are you going to choose?

Outdoor silage clamps - with great headroom

The answer to that question all comes down to cost. And because your farm is a business, then the answer to almost every question should come down to cost. And you’ll know if you’ve read any of the other blogs in this series, the cost isn’t the price you pay on the invoice.

So what is the cost of a silage clamp roof?

Well some of what makes up the cost is the price of steel rafters, bracings, purlins and roof sheets and the prices of these ebb and flow with the costs of the raw materials. These figures have been all over the place recently but at the time of writing budgeting £100 - £130 per square meter is a fair guide. So on a good sized clamp that might be £75,000 to cover a 1,500t clamp - that’s £50 per tonne stored!!!!!!!

Silage clamp buildings by RE Buildings

Only it isn’t is it, because the roof will be there for at least 20 years. Doing some quick maths that makes it £2.50 per tonne per year. Now that’s not quite so scary but it’s still not an insignificant sum. Hopefully a roof over the clamp offers you some advantages in reduced costs down the road. One of those significant costs is keeping the rainfall off your precious silage crop. In terms of dealing with just the rainwater run off, that dirty water would have to be spread from an open clamp, so you would be looking at about £750 per year to spread it. So that’s 50p per tonne of silage stored just to spread the rainwater every year.

Pumping rainwater is expensive

A roof on the silage clamp certainly reduces the chances of a pollution incident caused by monsoon rainfall. If you were to factor in the fines and solicitor’s fees were the worst to happen, then the roof suddenly looks cheap. Whilst this might be the biggest potential saving, there are better savings to be weighed up…. о

The biggest hidden cost from making silage are the losses that you never see. By having a roof over the clamp, these losses should be reduced. These are reduced by the shading effect of the roof that, in turn, reduces the microbial activity of the (mostly) undesirable bugs. This should mean the silage stored in a building is more aerobically stable. Aerobic losses can be as much as 40% of the silage feed value. By reducing the aerobic losses by just 5%, you can save yourself some valuable nutrients.

How do you cost in clamp losses?

This is a really important issue to consider. You could just say that the silage feed value you lose is (in this example) 5% of the total costs of making the silage. But assuming you need to replace that loss with something else, then the cost is considerably more than the 5% because the silage you feed is probably the cheapest nutrients in the ration. For example replacing a pounds worth of ME from silage with ME in barley is going to cost about two pounds. It costs you two pounds to replace them ME, but don’t forget you spent the money making the silage in the first place so the true cost of that lost ME is about three times the cost of the silage at three pounds.

Assuming a 30% DM silage with an ME of 11.5, that cost you £36 per tonne to produce (and it’s probably much more expensive than that) then the 5% saving in losses might be worth £5.40 per tonne! Even if you don’t factor in the cost of replacing the feed value, the 5% reduction in losses is worth £1.80.

All of a sudden, that cost of £2.50 per tonne to roof the clamp isn’t looking too ridiculous. That’s before you even start to think about the potential to store other things in space when its not in use as a silage clamp - things like high yielding vehicles such as caravans.

Should every clamp have a roof then?

Should every clamp have a roof then?

No that’s not what I am suggesting. Just like the convertible Mercedes, there are days when you just don’t want that roof. Sometimes the roof is a real pain in the neck because the building you could just about tip an 8 tonne trailer inside, is suddenly a “complete f…… nightmare” when you have 18t trailers queuing up to tip outside. And the MF 135 that used to roll the clamp has long since been replaced with a 6155R that just doesn’t quite slip under those roof beams so easily. So it's not really surprising that most silage clamps built in the last few years tend to be “outdoor clamps”.

What I am arguing is that you need to be constantly reviewing the options and keeping an eye on the cost of things. The price, the cost and the value are not the same thing. Find out the price, work out the cost and weigh up the value. Then decide if the roof you want to put on the clamp is at a price that’s worth paying.

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