Floor structure having sound attenuation properties
The floor structure has a base layer fastened to floor joists, a resilient layer laid over the base layer, and a top layer mounted over the resilient layer. The top layer has a stiffness that is greater than a stiffness of the base layer. The top layer is fastened to the base layer by wood screws that are placed substantially along a median between two adjacent floor joists. Each screw has a threaded portion extending simultaneously in both the top and the base layers. The installation of screws through the top and the base layers causes a backlash in the advance of the screws upon entering the base layer, thereby causing the occurrence of a larger gap between the layers as compared with an installation using nails. The larger gap relaxes a pressure on the foam layer and reduces the transmission of sound energy to the joists.
This invention pertains to floor structures having sound attenuation properties, and more specifically it pertains to a floor structure having vibration dampers incorporated therein.
BACKGROUND OF THE INVENTIONAt the present time, the National Building Code of Canada asks for a sound attenuation of 50 decibels through the walls separating apartments in a multi-apartment residential building. This standard is now under review, however. The Canada Mortgage and Housing Corporation for example, recently published sound attenuation objectives of over 55 decibels through walls and hard floors separating residential apartments, and over 65 decibels through carpet-covered floors. These objectives apply to sounds originating away from the floor, referred to as airborne sounds, and sound originating from the floor surface, referred to as impact sounds.
While several known floor structures can meet the requirement for airborne sound attenuation, the objective for impact sound attenuation has been a serious challenge in the construction industry.
The only prior art found disclosing a floor structure for minimizing impact noise transmission is the U.S. Pat. No. 3,270,475 issued to M. J. Kodaras on Sep. 6, 1966. This structure comprises a base layer made of low density material, fastened to the floor joists. Spaced-apart nailing strips are laid on the base layer perpendicularly to the floor joists and are retained to the base layer by spacer strips which are nailed to the base layer. The spacer strips have bevelled edges and define with the base layer spaced-apart dovetail slots in which the nailing strips are held without nail. The top flooring strips are nailed to the nailing strips with the nails not traversing the nailing strips. As the nails which secure the flooring strips to the nailing strips are completely isolated from the joists, there is no direct transmission of sound energy to the joists.
Although this document does not mention specific impact sound attenuation measurements, it is believed that this type of floor structure has great merits. This particular floor structure, however, is difficult and expensive to build by modern-day construction practices. It is believed that this difficulty constitutes a main reason, basically, why this method has not enjoyed a lasting commercial success.
Also, there is a trend in the construction industry to use 24 inch joist spacings as opposed to the long lasting standard of 16 inch spacings. The larger spacing requires more rigid floor and sub-floor layers. This trend motivates builders to combine rigidity and sound transmission attenuation performances in building systems.
As such, there is a need in the construction industry for a floor structure having acceptable sound attenuation characteristics without imposing a burden on existing construction trends and practices.
SUMMARY OF THE INVENTIONIn the present invention, however, there is provided a floor structure that is compatible with modern-day construction practices with a joist spacing of 24 inches. The floor structure according to the present invention has an airborne sound attenuation of 65 decibels and an impact sound attenuation of 56 decibels. These sound transmission measurements were confirmed by the Acoustic Institute of the National Research Council of Canada.
More specifically, the present invention comprises a floor structure having spaced-apart floor joists, a base layer fastened to the joists, a resilient layer laid over the base layer, and a top layer mounted over the resilient layer. The top layer has a stiffness that is much greater than a stiffness of the base layer. The top layer is fastened to the base layer by wood screws which are placed substantially along a median between two adjacent floor joists, and each wood screw has a threaded portion extending simultaneously in both the top layer and the base layer.
The installation of the wood screws through both the top and the base layers causes a backlash in the advance of the screws upon entering the base layer, thereby causing the occurrence of a larger gap between the top layer and the base layer as compared with an installation using nails for example. The threaded portions of the screws being engaged simultaneously in both the top layer and the base layer act as spacers between the top layer and the base layer. The larger gap relaxes a pressure on the foam layer to reduce a transmission of sound and noise energy between the top layer and the joists.
In another aspect of the present invention, the top layer is made of balsam fir boards having a thickness of about 2 inches, and the base layer is made of oriented fibre boards having a thickness of ¾ inch. The balsam fir boards have a width of 24 inches, a length of 16 feet, and tongue-and-groove edges. The floor structure according to the present invention is very strong as compared with common floor structures, and is particularly appropriate for use with low-deflection flooring surfaces such as ceramic tiles.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGSOne embodiment of the present invention is illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will be described in details herein one specific embodiment of a floor structure with improved sound attenuation properties. The present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiment illustrated and described. For example, precise dimensions are used herein for convenience only to provide a better understanding of the structure of the present invention. Such dimensions should not be considered as being absolute and limiting.
Referring to
A second layer 24 made of resilient material is laid on the base layer 22. The second layer is made of foam sheeting, geo-textile, rubber, felt or a similar material and has a thickness of about ⅛ inch. This second layer 24 is fastened to the base layer 22 in a conventional way, with staples for example. For economical reasons, the second layer 24 in the preferred embodiment is made of foam sheeting and is referred to herein as the foam layer 24 for convenience. The purpose of this second layer 24 is to prevent hard contact region or direct contact point between the base layer 22 and the top layer 26.
The top layer 26 is laid on the foam layer 24, and is fastened to the base layer 22 with wood screws 28 extending along medians 30 between adjacent joists 20 such that there is no direct transmission of sound energy from the top layer to the joists.
The top layer 28 is made of wood boards 32 having a thickness of 2 inches; a width of 24 inches and a length of 8 to 16 feet. The wood boards 32 are made of balsam fir and have a tongue-and-groove profile along their edges. The fir boards 32 are made of three plies with a different fibre alignment in the middle ply, as it is customary in plywood boards. This type of wood board is described in Applicant's Canadian patent application #2,434,248, filed on Jul. 3, 2003.
The two inch thick fir boards 32 have a moment of inertia which is about 32 times greater than a ⅝ inch sheet, and about 18 times greater than a ¾ inch panel (proportional to the cube of the thickness). The stiffness of the fir boards 32 is therefore greater than the stiffness of the base layer 22 by about the same proportions.
The principal contributing feature to obtain the sound attenuation properties of the floor structure according to the preferred embodiment of the present invention will now be explained while making reference to
In
It will be appreciated that because of the engagement of the threaded portion in both the fir board 32 and the base layer 22, the screw cannot pull the base layer 22 against the fir board 32 at the end of its insertion. The screw segment ‘A’ traversing the foam layer 24 remains in compression to retain the top layer 26 at a distance from the base layer 22.
The combination of the thread backlash, the foam layer 24 and the long threaded portion of the screw 28, causes the occurrence of a joint 36 that has spacing and vibration-absorbing properties as illustrated schematically in
Because of this type of joint 36, the base layer 22 is pre-stressed at every screw 28. Under no load condition, the base layer 22 springs back straight and pushes the top layer 26 upward, to release a compression in the foam layer 24. Because of this type of joint 36, it is believed that an impact force on the floor surface is partly absorbed by the deflection 42 in the base layer 22. It is also believed that a load on the top layer 26 is partly absorbed by a deflection 42 in the base layer 22 before a pressure is applied to the foam layer 24 in a region 44 above each joist 20 for example.
It is believed that sound transmission is effected primarily along these regions 44 above each joist 20 when the floor is loaded. It is also believed that the relaxation of pressure on the foam layer 24 due to the thread backlash or gap ‘A’ in each joint 36 contributes significantly to obtain the sound attenuation properties observed in the floor structure according to the preferred embodiment.
The sound attenuation properties referred to herein will be better understood when making reference to
Another common type of floor structure, as illustrated in
Tests on the floor structure according to the preferred embodiment, however, have demonstrated that the sound attenuation properties of this preferred structure are 65 dB for airborne sounds and 56 dB for impact sounds. It will be appreciated that the sound attenuation properties of the floor structure according to the preferred embodiment exceeds the proposed requirement of 55 dB for both sound sources. It will also be appreciated that the high stiffness and relative low density of the floor structure according to the preferred embodiment allow for wide span of 24 inches or more between joists.
Referring now to
During this initial drilling of the surface of the OSB™ or plywood layer 22, the engagement of the thread into the fir board 32 causes the screw 28 to continue to advance at a constant rate of speed. Consequently, a pressure is applied on the tip 34 of the screw and against the base layer 22.
Because the stiffness of the fir board 32 is much greater than the base layer 22, the base layer 22 is caused to move away from the fir board 32, one or few thousands of an inch or maybe more. When the screw 28 resumes its advance into the base layer 22, a small gap ‘A’ remains between the base layer 22 and the fir board 32.
Because of such screw backlash between the fir board 32 and the base layer 22, and because the screw 28 has thread engagement in both the fir board 32 and the base layer 22, the screw 28 constitutes a spacer for separating the fir board 32 from the base layer 22. Such a spacer means is represented by a block-type spacer 38 in
Because the fir boards 32 are much more rigid than the base layer 22, a loading on the floor structure deflects the base layer 22 before the fir boards 32, and before the fir boards 32 can apply a pressure on the foam layer 24 above the joists 20, as indicated by the regions 44. The base layer 22 acts as a shock absorber or a suspension system to support the fir boards 32 in a floating mode above the foam layer 24 and the joists 20.
As to other manner of usage and operation of the present invention, the same should be apparent from the above description and accompanying drawings, and accordingly further discussion relative to the manner of usage and operation of the invention would be considered repetitious and is not provided.
While one embodiment of the floor structure according to the present invention has been illustrated and described herein above, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. For example, it is known that similar advantageous results can be obtained with screws other than common wood screws, as long that their threaded portions extend simultaneously in the base layer and the fir boards. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention.
Claims
1. A floor structure for attenuating impact and airborne sounds, said floor structure comprising spaced-apart floor joists, a base layer fastened to said joists, a resilient layer laid over said base layer, and a top layer mounted over said resilient layer;
- said top layer having a stiffness greater than a stiffness of said base layer;
- said top layer being fastened to said base layer by wood screws; said wood screws being placed substantially along a median between two adjacent ones of said floor joists, and each of said wood screws having a threaded portion extending simultaneously in both said top layer and said base layer.
2. The floor structure as claimed in claim 1, wherein said top layer is made of balsam fir boards each having a thickness of about 2 inches, and said base layer is made of oriented fibre boards each having a thickness of ¾ inch.
3. The floor structure as claimed in claim 2, wherein each of said balsam fir boards has a width of 24 inches, a length of 16 feet, and tongue-and-groove edges.
4. The floor structure as claimed in claim 3, wherein said floor joists are spaced 24 inches apart.
5. The floor structure as claimed in claim 1, wherein a stiffness of said top layer is 32 times greater than a stiffness of said base layer.
6. The floor structure as claimed in claim 1, wherein each of said wood screws also has a segment traversing said resilient layer and said segment is in compression for preventing a collapsing of said resilient layer.
7. A floor structure for attenuating impact and airborne sounds, said floor structure comprising spaced-apart floor joists, a base layer made of ¾ plywood and fastened to said joists, a resilient layer laid over said base layer, and a top layer mounted over said resilient layer;
- said top layer having a thickness of 2 inches and being made of three plies with wood fibres in a middle ply oriented at right angle with wood fibres in outside plies;
- said top layer being fastened to said base layer by wood screws; said wood screws being placed substantially along a median between two adjacent ones of said floor joists, and each of said wood screws having a threaded portion extending simultaneously in both said top layer and said base layer.
8. The floor structure as claimed in claim 7, wherein each of said wood screws also has a segment traversing said resilient layer and said segment is in compression for preventing a collapsing of said resilient layer.
9. A floor structure having an impact-sound attenuation properties better than 55 dB, said floor structure comprising floor joists spaced at 24 inches apart, a base layer having a thickness of about ¾ inch fastened to said floor joists, a resilient layer having a thickness of about ⅛ inch laid over said base layer, and a top layer made of balsam fir boards mounted over said resilient layer;
- said top layer having a thickness of 2 inches, and being fastened to said base layer by wood screws; said wood screws being placed substantially along a median between two adjacent ones of said floor joists, and each of said wood screws having a threaded portion extending simultaneously in both said top layer and said base layer.
10. The floor structure as claimed in claim 9, wherein each of said wood screws also has a segment traversing said resilient layer and said segment is in compression for preventing a collapsing of said resilient layer.
11. The floor structure as claimed in claim 10, wherein each of said balsam fir boards has a width of 24 inches, a length of at least 8 feet and tongue-and-groove edges.
12. The floor structure as claimed in claim 11, wherein said base layer is made of oriented fibre boards.
Type: Application
Filed: Feb 9, 2006
Publication Date: Aug 23, 2007
Inventor: Guy Gilbert (Sainte-Foy)
Application Number: 11/349,996
International Classification: E04F 15/22 (20060101);