Design collection for a double storey house with rat trap ...

English text

Skat ref n…°

Compiled by Ph.P.

Edited by Sanu Babu Dangol

DESIGN COLLECTION

Double storeys house with Cavity

BrickWall technology

CASE – Peri-Urban House in Rusizi

Design Collection for a double storey house with Cavity brickwall Building system

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CONTENT

1. Introduction .................................................................................. 4

2. CBW HOUSE MAIN CHARACTERISTICS ............................................ 5

3. Key features of the Cavity brickwall ............................................... 6

4. Bonding Principle of Cavity brickwall Masonry ............................... 7

5. RULES FOR JOINT ........................................................................... 7

6. Main advantages ........................................................................... 8

7. Main Disadvantages ...................................................................... 9

8. Specific CBW Masonry rules ........................................................... 9

9. APPLICATION............................................................................... 10

10. OBSERVATIONS ............................... Error! Bookmark not defined.

11. SOURCE & BIBLIOGRAPHY ........................................................ 40


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1. Introduction

Cavity BrickWall masonry has been used to construct a small

double storeyed residential/commercial building in load

bearing construction, using the specific construction details

which are followed in this leaflet.


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2. CBW HOUSE MAIN CHARACTERISTICS

The outer dimensions of the House are :

….m long, …..m wide and ……..m high

• Structure: CBW load bearing wall

• Dimensions: 90 m2 in two storeys

• Dim. of standard brick: 210 x 100 x 55 mm

• Number of bricks: 85 -90 /m2

• Cement: 8.5 Kg / m2

• Cement/Sand ratio: Vol 1:4

• Employees: ……………………….

Front View of the House on construction phase


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3. Key features of the Cavity brickwall

The Cavity brickwall is a type of wall brick masonry bond in

which bricks are laid on edge. This gives the wall with an internal

cavity bridged by the transversal brick disposal. Is a proven

economical walling bond with good insulation properties due

to the air cavities.

The use of CBW compared with ordinary English bond has an

impact on several fronts;

Economic: It saves up to 30% on bricks and up to 50% on

cement mortar.

Environment: 1 m2 of CBW uses 130MJ less energy and

emits30kg less CO2 than English bond.

Skill Enhancement: it enhances the skill of masons by requiring

them to construct a modular wall with a neat finished

appearance


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4. Bonding Principle of Cavity brickwall Masonry

The Bonding principle of the Cavity brickwall is always

governed by the Brick Cross which is formed by the alternation

of “Shiner” brick and “Rowlock” as per the figure above.

5. RULES FOR JOINT

Mortar

The principal requirement for rat-trap

brickwork is the availability of good

quality bricks. The ultimate strength of

masonry depends on the brick quality

and the bond strength between the

bricks. The mortar joints are the weakest

as well as the most expensive part of the

masonry

For a one-storey load bearing building1:6

mortar ratio is recommended

For a two-storey load bearing building1:4

mortar ratio is recommended (1:6 upper

level)

For Horizontal “bed” joint a thickness of

12mm is recommended to ensure:

Levelling

Placing the brick completely in the mortar


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No uneven or incomplete support of the bricks

For Vertical joints “Cross joint and Collar joint” a thickness of

10mm is recommended

NB: to ensure that vertical joint is fully filled with mortar, masons

must apply the joint mortar direct onto the brick before laying

the brick

BRICK SOAKING

Before brick is placed it needs to be thoroughly soaked in water

to clean from dust and to verify it is not too porous.

Maximum wall height per day

The maximum Cavity brickwall brick wall height per day should

not exceed more than 9 layers. The added weight by each

new course needs to be carried by the mortar. The mortar

however needs to harden and carry the load without

developing cracks

Curing

A brick wall need to be cured for at least 7 days. Several times

a day water needs to be poured over the brick wall.

Pointing

Pointing can be carried out to give neat finish to the work and

to increase its weather resistance (especially in freezing

conditions)

Adoption

As the CBW uses a high proportion of “Shiners” (bricks disposed

longitudinally) alternately to transversal bonding ones, for load

bearing walling is recommended to don’t go over three stories.

As a filler wall between a structure frame there is no limitation

on height.

6. Main advantages

Main advantage is the economy of bricks:

Using this method of bonding it is possible to use:

approx. 35% less bricks than an English bond masonry


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50% less cement mortar than an English bond masonry

Meaning reducing the price of a 21-23 cm wall by 30%

Thermal comfort for its cavity core in the middle (interiors

cooler in winter and warmer in winters)

Aesthetically pleasing wall surface (plastering can be

avoided)

All concrete work (pillars, sill bands, window and tie beams

can be concealed and hence only brick masonry work is

exposed) as per figure above.

The walls have approx. 20% less dead weight and hence

the foundations, depending on the bearing capacity of

the soil, can suitably be redesigned to save bricks, steel and

cement.

Vertical wiring and plumbing can easily be made during

the wall construction and even after since the cavities

allow inserting the fittings

CBW is a modular masonry system which can reduce

wastage of bricks by un-necessary cutting.

7. Main Disadvantages

Main Disadvantage of the Cavity brickwall is that it has to

be made by well trained and skilled masons.

Although this should be seen as an opportunity to get

specific skill thus led to sectorial labour market

8. Specific CBW Masonry rules

Only good quality fired bricks without cracks nor

deformations must be used


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Only bricks of the same dimensions should be used

For proper alignment of the CBW wall, masonry strings must

be used at both sides of the wall

The vertical joints must be applied directly to the brick before

placing it

A “brick Cross” must be maintained at all time for a proper

CBW masonry wall

Cavities of TRB masonry must be closed. Following must be

solid: First course after DPC; Sill Level; Lintel Level; Top most

Course

Total wall height must be divided into appropriate number

of brick layers in order to maintain a uniform horizontal

mortar joint thickness; Accordingly the height of openings

must be in multiples of the rattrap course height to avoid

incorrect details at the lintel level

To improve earthquake resistance the CBW walls must be

reinforced with 12mm steel bars at all corners, openings

(doors and windows) , T-junctions and filled with a M20

concrete. Earthquake resistance will further improve if a

vertical steel bar is inserted at every 1m distance and filled

with a M20 concrete. Reinforced tie-concrete bands should

be provided at three levels: Sill, Lintel, Roof level (in case of

load bearing structure)

In areas with high ground water table it is advisable to build

the first 40 -50 cm if the walls with either English or Flemish

bond, to avoid ground and spill water related dampness

problems

A wall shall be designed such as local bricks size can be used

9. APPLICATION


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Foundation plan and section – Notice due to the reduced weight of the load

bearing system wall, the thickness of the foundation, thus the component

material required, are reduced of 20% in comparison with standard structure


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Stone Foundation View – Notice the raised level of the ground beam


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Detail of the foundation – Notice the starting level for CBW brick layering in

relation to the ground level


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Foundation detail view – Notice the rubble stone masonry on bottom and

the levelling ground beam on top where to start layering the brick - course

Ground beam layout plan – B.L – 0.13 m and TL +- 0.00m


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Rat Trap Layer 1and 2 of ground floor – The first layer of CBW is very critical

and require much attention: Following courses and will depend on it


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Details of the corner solutions – Each critical point of the structure has to be

properly conceived in design phase and fit out with the contextual brick

succession while layering on site

Notice the reduced size of reinforced concrete needed as structural jointures

Technical Experts shown locally formed masons how accuracy has key role

in respecting design layout solutions


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Typical Rat Trap Layer 1 & 2 – Notice the interlocking accurate disposal of

the bricks in the alternation of courses of “Rowlocks” and “Shiners”


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Other details of critical joints

Expertise is required to follow first steps in this building technology as different

solutions have to be found following design characteristics. Once local

masons are getting use with the system, they themself will teach others about

correct behaviour in CBW building


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Concrete Beam Details


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Layout

Ground floor plan

The layout of the two

storey house has

been drafted for a

family use.

It has been

conceived with living

area on ground floor

and services (kitchen

+ toilet) on external

annex in the private

garden.

In the ground floor a

small shop (dim.

3.2m x 4.6m) with

entrance through a

little porch facing

the public square

and possibility to

communicate with

the private

residential part, has

been placed.

Comunication

towards the second

floor (bedroom

area) is through a

central staircase


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Raising of the ground floor walls. Not more than 9 courses of bricks should be

laid per day in order to not overload the fresh mortar and avoid layering

distorsions. Notice the porched area in front of the frontal openings

Ground floor Sill level - BL +0.77 m and TL +0.88 m


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Ground floor Lintel Layout plan –

B.L +2.09 m and TL +2.20 m at axis A-A, TL +2.30 m


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Layout

First floor plan

The two bedrooms

(dim 3.5m x 4.6m) on

first floor are

reached through a

central staircase.

A small veranda has

been set on top of

the porched area.


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First floor Lintel Layout plan –

BL +4.84 m and TL +4.95 m


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Section XX –


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Detail joint CBW wall –1st floor beam – Notice: 2 solutions has been

experimented for the different situation of anchoring the1st floor structure

with the load bearing CBW walls


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Timber beam section and layout plan in1st floor slab


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Timber beam details of the joist


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Timber beam layout zoom


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Section Y1Y1


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Section Y2Y2


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Stair Section – Notice: its structure will be self supporting

Stair Details


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Roof Beam Detail

Roof Beam Layout plan


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Rafters Layout plan

Rippers Layout plan


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Roof Section XX


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Roof Structure Details


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Side view of the house - Notice that CBW system allows whole brickworks

façade concealing concrete structures within its loading bearing thickness

wall.


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Front Side of the House with Shop on the bottom


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10. SOURCE & BIBLIOGRAPHY

Principle of Rat Trap Bond Module A9 - VSBK/CESEF

Project Nepal


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This leaflet has been edited by:

With the financial support of:

Design collection for a double storey house with rat trap ...

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