Does inter room noise transmit via a ceiling space?

[epsilonGreedy]

I am thinking of deviating slightly from my technical drawings but before doing so I am wondering if noise attenuation over the top of an internal block wall is the motivation for the current drawn design.

 

In the diagram below the internal block wall, between entrance hall and the downstairs toilet, is half a block higher than the main external wall wallplate.

 

I intend to build the wall only up to the wall plate height of the external walls which will make it simpler to add some ceiling joists across the 1m width of the toilet. These joists are needed because this section of the ceiling is under the hip end and hence missing the truss joists to fix plasterboard to. If the internal dividing wall is topped off with some wooden wall plate then the ceiling joists can be laid across both the external wall and internal wall wallplates between the two arrows and anchored with some metal framing clips. 

 

Am I missing any good reason for building the internal wall just above ceiling plasterboard height, possible noise attenuation?

 

 

Edited September 20, 2021 by epsilonGreedy

[saveasteading]

I am finding it tricky to read the logic of this design. I would expect to see the sloping truss sitting on the wall you are discussing, but it seems to be hanging, or there need to be cut-outs in the wall for the truss and beam right through the width.

Your idea seems better, but perhaps I am misreading.

[epsilonGreedy]

1 hour ago, saveasteading said:

I am finding it tricky to read the logic of this design. I would expect to see the sloping truss sitting on the wall you are discussing, but it seems to be hanging, or there need to be cut-outs in the wall for the truss and beam right through the width.

 

 

Well spotted, at the moment the sloping truss is "hanging" there because the top block is missing. Currently it is supported by metal cup (sic) hanger attached to the side of the doubled truss under the end of the ridge.

 

You are right, if I follow Plan-A as per the diagram I will need to run that sloping truss through a gap in the final course when laid. With my Plan-B I will need to slip a length of wall plate under it as I finish off the internal wall at a lower height. I want to do this before the roof is loaded with the weight of the natural slate covering. I expect the wooden roof structure will bow a few mill under the extra weight and so the sloping truss will contribute to the over all support.

 

Err just going outside to check there is a vertical timber in that truss above the partition wall.

 

Ok Back. No there is not. I need a Plan-C.

 

The horizontal gap between the double truss and the partition wall by the right hand-drawn arrow is about 120mm. The ceiling level horizontal element of the sloping truss is slender probably 75mm x 38mm with no vertical timber immediately above. Hmm not good. That could be stressed too much if it sits tightly on top of the partition wall before the weight of the roof cover is added.

 

Thinking, thinking...

 

Plan-C.

1. Ignore the official drawing, finish the partition wall with a wooden wall plate at a matching height to the external wall.
2. Fix the independent ceiling joists over the toilet before the roof is felted because with a 30 degree slope it will be a pain to fix these to the external wall plate from the inside once the roof is covered.
3. Augment the sloping truss with an extra vertical timber 122mm x 38mm aligned above the partition wall.
4. Before bedding down the partition wall wallplate ensure the sloping truss floats just above wall plate without the roof covering weight, route wallplate if necessary.
5. Fix the slates to bring the roof up to final full weight.
6. Observe the remaining floating gap under the sloping truss for a few months.
7. When everything has settled and the wooden roof structure has fully sagged, knock a few opposing wooden wedges between the sloping truss and partition wallplate so that the partition wall contributes 20kg to 30kg of support to the hip end of the roof.

 

Roof weight calc:

The average slate weight is 1.7kg.

Roof area is 16m2

Slates per m2 is 19.5

 

Therefore total roof weight is 19.5 x 1.7kg x 16m2 = 0.53 ton + 50kg lead ridge.

 

Assume 1/3 of roof weight is in the hip end and 1/3 of the hip weight sits outboard of the wallplate thus canter-levers another 1/3 of the hip weight. I therefore I conclude the central weight of the hip that needs support is 60kg to 100kg. So not much to worry about ( the jack rafters are now at 300mm centres ).

 

 

Edited September 20, 2021 by epsilonGreedy