Sound Insulation for Garden Office

[gunnag]

Hi All,

I would like to know what materials will help reduce road noise in my garden home office currently under construction.

The office is about 100ft away from a busy motorway and was previously a timber framed lean to pergola with a 16mm triple wall poly-carbonate roof converted to an office. The office has 2 external walls and I guess these together the roof are where motorway sound is coming from.

The construction started by adding 2x4 timber studs to the existing pergola, then ½ inch OSB was screwed to the outside. The stud work was filled in with 75mm of PIR foil faced insulation and sealed with foam around the edges.

A breathable membrane was added to the outside of the OSB and a PVC dpm used over the stud-work internally and on the floor.

The floor consists of the existing concrete base with 75mm EPS foam added, then 18mm t & g chipboard.

Next we added ½ inch acoustic plasterboard to all the walls screwed on to the studs. A upvc French Door was fitted and the plan is to add tongue and groove log lap cladding to the exterior.

Currently the noise reduction is not sufficient and I don't know how much the log lap cladding will help when added. The log lap will be laid on battens to allow air flow.

Does anyone have ideas for improving sound insulation from the motorway? Some of my thoughts are as follows:-

• add a second later of acoustic plasterboard with a 2mm rubber sheet in between. I've read that this works really well. Do all 4 walls need this treatment or just the 2 exterior walls?
• add a layer of 12mm OSB on the exterior battens before adding the log lap cladding. Perhaps a layer of 2mm rubber could be sandwiched between the OSB and cladding?
• Regarding the triple wall poly-carbonate roof, I can only think of infilling the space between some of the rafters with rockwool sound insulation and then adding acoustic plasterboard as a ceiling. Currently all of the ceiling is poly-carbonate so may have to add sound insulation to an area around the edges (30% ?), so some light will be lost.

Thoughts and comments welcome.

 

[mikeey84]

I'm no expert, but from what I understand with that roof, you will really struggle, regardless of what you do to the walls.

Noise reducing is a complicated area, and there are a few threads on the forum that go into the science of it

Road noise from a motorway is quite different from trying to insulate yourself from noisy neighbours.

What do you have between the building and the road itself?

 

[^woody^]

Plasterbaord stops noise getting out not in. You need mass in the structure and on the outside, and no air gaps, and certainly no plastic roofs.

Sound insulation should be designed in at the start not added ad-hoc (eg rockwool not PIR). Your options are limited so don't expect much based on what you have, and adding this or that in the hope of an improvement would be a waste of time. The cladding will help as long as it's well fitted timber and hardwood like cedar will be better than SW or anything else.

Your roof is a massive problem and can't be compensated by any improvements elsewhere.

 

[gunnag]

Thanks for the comments, I agree that the roof is the main problem but it looks like there's not much that can be done, short of retrofitting a real tiled roof with appropriate sound/heat insulation.

Between the motorway and the house there is already a sound proof fence supplied by the Dept of Transport and also a row of conifers. I was thinking about building some kind of stone filled gabion at the end of the garden to help reduce noise but thats just a dream for now.

In retrospect it would have been better to have used rock-wool sound insulation between the studs. When I came up with the design I was concentrating on thermal rather than acoustic properties, so now I know better.

Interestingly I've noted that when the sun shines, the room heats up rapidly to 20c even when its less than 10c outside. The poly-carbonate roof is bronze which is supposed to reduce heat build up but I can forsee the room getting unbearably hot in the summer months, so thats another problem to resolve going forward.

I haven't chosen the exterior log lap material yet and was going to use Scandinavian Redwood tongue an groove. I will look into using cedar if it works better and also maybe Siberian larch.

For info I downloaded a noise level app on my phone and found the sound level inside the office is around 51Db whilst outside its about 63Db, hopefully the cladding will result in further reductions.