Reducing road noise outside?

mbi15, Oct 26, 4:35am
We live on a main road SH26 on the outskirts of a town. It would be great to reduce some of the road noise outside so its not so intrusive (have double glazing on windows, so inside is not too bad).

We have a 150high wooden fence, but it has a couple of gaps in it.

Just wondering if there is some easy residential solutions to road noise? The only thing I can find is a concrete block fence, but it would need to be at lease 40-50m long which will be quite expensive.

perfectimages, Oct 26, 4:46am
Tall shrubs and trees are used by a lot of people including the likes of NZTA, for noise reduction all over the world. Usually a quite dense planting.

lakeview3, Oct 26, 4:50am
There are a couple of houses here on a main road. One has mounded a huge long pile of dirt snd planted with flax, another has used stacked tyres. The stacked tyres look quite good actually as they have filled them with dirt and planted plants that cascade down them in them. It s a good idea because that particular house has had at least 3 vehicles crash through its front yard that I can remember. Safer for the people in the cars than a concrete wall as well.

You could do this on the inside of your fence and plant a row of pittosporum on the outside by the road?

mbi15, Oct 26, 5:15am
Its pretty difficult to get to the other side of the fence cause its a bank down to the road (road goes down hill), there are some Pittis there and Ivy on that side.

lakeview3, Oct 26, 5:31am
so you are uphill from the road? Yes unfortunately sound does travel up. In that case you could try to install the tyres on the inside of your fence and if you find them ugly then you can plant pittos in front of them so you don’t have to look at them.

Hey, at least the tyres are free!

tweake, Oct 26, 6:56am
a lot of that is for noise reduction for the people on the road, not people living near by. plants tend to dampen the sound not get rid of it.

as mentioned above the main thing to stopping the sound is large amount of mass and reflecting surfaces. big earth banks work great.

perfectimages, Oct 26, 7:12am
I did say noise REDUCTION I did not mention getting rid of noise completely, that is a different kettle of fish. Anything that will reduce the transmission of noise is surely a help in the OP's situation. and I happen to disagree with your assesment that the idea of planting is mainly for the benefit of the people using the road, as all over the world (including here) I have seen plantings at the side of motorways designed to reduce noise to adjacent properties.

bill-robinson, Oct 26, 7:43am
look to deflecting noise sloped fences that sort of thing. banks are brilliant but costly.

tweake, Oct 26, 8:06am
a lot of the planting is on banks.
its the bank that does the bulk of the noise reduction. plants are often primarily used for erosion control. people behind the bank won't hear much with or without plants. however the noise reflecting back towards the road by the bank is reduced a bit by the planting.

planting on its own, say on the level, does very little noise reduction. to many gaps and generally no where near thick enough. its useful but only when combined with other measures, like earthworks.

perfectimages, Oct 26, 9:42am
tweake; Maybe you did not read the OP's last paragraph at post #1.
you seem to be advocating that they build a high bank at the border of their property and the road, which to my mind, does not meet their requirements of an "easy solution". Such a solution would probably be out of the question as far as being a practical solution and would be extremely expensive. So I still suggest a planting dense enough to, at least, disrupt the direct transmission of the road noise

tweake, Oct 26, 10:18am
i have people near here who did exactly that. had digger on site, not hard to do.
all depends on what you call easy or expensive. a stacked tire wall filled with dirt is reasonable easy. even a sand bag wall works well. anything that is heavy and continuous.

the problem with trees is its just so ineffective for the cost and time it takes. the space requirements and cost of trees is rather large, especially when your talking years before they get big enough to do anything.
your not talking about a simple hedge row.

no problem with a solid wall with trees in front, that works well.

amasser, Oct 26, 10:37am
Believe this to be correct as they disperse sound waves, whereas hard surfaces bounce them around. An audio engineer could comfirm.

tweake, Oct 26, 11:23am
trees are mostly hard surfaces. bound to be some sound absorption but also a lot of reflecting. but its reflecting it in a wide range of angles.
however that only really works for high frequency. low freq can go almost straight through. this is where a solid mass comes into play.
a solid mass reflecting the sound in one direction is fine if that direction is away from you. kinda sucks a bit if your the one its reflecting to.

gpg58, Oct 26, 2:41pm

tegretol, Oct 26, 4:37pm
There really is no single easy answer.

My neighbour had the same issue on SH6 and a 3m high bund partially solved it. The roadside slope is at 35 degrees and the inside slope at about 70 degrees (it is partially held with a retaining wall 1200 high).

I took some good averaged dBA and dBB measurements over three months prior to him building the bund and then repeated that after the job. Overall, there was average reduction of around 8dB.

But in my own house, fitting extra double glazing (to end up with triple) glazing gave us 10dB of reduction and now we can hardly hear the traffic (the house is 30m from the highway). So I reckon my solution was a cheaper one!

tegretol, Oct 26, 4:41pm
I just love the diagram in paragraph 1.3 that outlines which 'experts' need to be involved.

By the time you'd paid all of them, you may as well sell up and move on.

hesian, Oct 27, 9:41am
Odd thought but would using cork and bamboo screen work? Read about cork being used in housing overseas recently. It was thicker than we can get here but maybe double sheets? I used to rent on noisy road and it was hard to dim it as landlords didnt want fencing though would allow temporary fencing. A couple of years on I would try that now and take it with me!

tweake, Oct 27, 9:53am
correct me if im wrong here but isn't 3db change half the volume?
so about 25% of the volume. not bad.

but i think you highlight the other factor and thats our homes. they are not made for noise suppression.

tho the other factor is type of noise. some noises re just plain more annoying even tho they are not loud.

cromergy, Oct 27, 11:34am
If you go for the planting option then look at Lilly Pillys (Eugenia Ventenati). They grow fairly quickly and look good all year round and much less maintenance that a pittosporum hedge. The best place to buy bulk affordable plants is Rogers nursery in Mangere Auckland. We bought some about 3 months ago and they are growing really well and were only $10 each. They will over time get top 6m X 4m w if untrimmed but they are a fairly soft wooded tree so easy to trim.

tegretol, Oct 27, 4:08pm
Where is the valid science that shows trees to be much of a sound reducer?

vivienney, Oct 29, 7:43pm
Wall insulation dulls strong sounds.

tygertung, Oct 30, 1:20am
Resurface the road with bitumen, less noise as it is much smoother.

brightlights60, Sep 13, 4:14am
We live on a main road coming into Christchurch (4 lanes). House is a way back and on 1M of concrete slab, with newer alluminium so quiet inside. We have been here over 20 years, first thing we did was build a "sound hedge", i.e. pitties and a few ake ake, lemonwood and broadleaf planted fairly close together. We let this grow to fence height and have it trimmed twice a year. The result is a very compact, dense, sound proof layer between us and the road. Added to that, all our fences are corrugated iron, which sound bounces off. I don't particularly like pitties, but they are a good hedging tree and fast growing. They are now just a few cms above the fences and give us privacy right around plus deaden the sound.