One of the very many defects in our Bovis home is alarming cracks in all four corners of the house. Bovis “fixed” these cracks, but as they kept reappearing despite these fixes, Bovis had a structural engineer inspect the roof. The structural engineer’s report is, of course, hard to read, but here are some excerpts from the structural engineer’s report:

The hip rafter was checked with an applied triangular load distributions as a
continuous beam and the lower section deflects 11mm, the upper section deflected
29mm these deflections are greater than the permitted deflection of (0.003 x 3400) =
10.4mm.
The hip rafter fails in deflection.

When checked as a beam restrained at 0.6m centres from laterally deflecting the
deflection was below the code requirement however, the timber became overstressed
by a factor of 1.62 and 1.70, for the lower and upper sections. The hip rafter is,
therefore, underdesigned.

When checked as a beam restrained at 0.6m centres from laterally deflecting the
deflection was below the code requirement however, the timber became overstressed
by a factor of 1.62 and 1.70, for the lower and upper sections. The hip rafter is,
therefore, underdesigned. (See Appendix D: R. Calculations pages 1-8).
The deflections of the lower and upper spans of the hip rafter when laterally restrained
reduce to 3mm and 8mm respectively.
The calculated deflection of the supporting blue truss (GT03) at its midspan is 21.3mm
(See Appendix C Pg.52. Calculations).
The deflection of the blue double truss GT03 2.5m from the front wall is (2.5 x21.3)/4.8
= 11.1mm.
When the two deflections are combined the deflection of the truss and hip rafters will
be 3.0 + 11.1 = 14.1mm, 8.0 + 11.1 = 19.1 both of which are beyond the permissible
deflection for the hip rafter (0.003 x 3.15 = 9.45mm). The hip rafter fails in deflection.

The lower deflection of 8mm has been obtained by calculation when the hip rafter is
restrained by the roof rafters either side of it. (See R. Calculations Pg.8).
See Appendix D: Pages 22-26. The hip rafter has been checked as a two span
continuous beam, with 2No. spans of 3,074m, the hip rafter fails in bending stress and
deflection, the permissible deflection is 9.34mm and the applied deflection is
12.96mm.

HIP RAFTER
Bearing onto Double Truss GT03. (See R. Calculations Pg 6).
Reaction of Notch = 7.42Kn
Area of Notch = 50 x 37mm
= 1850mm²
Bearing = 6.15 x 10³/ 1850
= 3.32N/mm²
BS5268-2 Table 9
Permissable Bearing for TR26 = 2.50N/mm²
401 > 2.50
The permissible bearing is exceeded, the joint fails in bearing.
The shear force at the top of the hip rafter is 3.76Kn.
From BS5268 T.61 for a 2.7mm diameter nail with a standard penetration of 32mm
the permissible shear load = 0.281Kn.
The No. of nails required for the joint = 3.76/0.281 = (14Nos)
We do not know how this joint is made but you cannot fit 12No. 2.7mm diameter nails
at code permissible centres through the hip rafter.

(See Appendix D: Pg 22-26) This shows that the hip rafter, checked as a continuos
beam fails in bending and deflection. However, the hip rafter has been loaded as a
uniformely distributed load, and when analysed no account of the propping action has
been taken.
ROOF RAFTER (SPAN 1.79M)
(See Appendix B: Drg No. 220818-SK2: Green colour)
(See Appendix D: Pg 5-8, 9-12 97 x 35mm (d x b) shows Grade of Timber TR26).
The 97 x 35mm roof rafters shown as green rafters. These have been checked and
they do not comply with current code requirements. The deflection of 5.72mm is
greater than the permitted deflection of 5.40mm.
The deflection of the supporting truss at mid span is 21.3mm (See Appendix C. Pg
53) The deflection of the double truss 1.8m from the front wall is (1.8 x 21.3)/4.8 =
7.98mm

Then if the two are combined the deflection of the rafters will be 7.98 + 5.4 = 13.33mm
which is beyond the permissible deflection.
ROOF RAFTER TO RIDGE (SPAN 1.79 + 1.79M CONTINUOUS)
(See Appendix B: Drg No. 220818-SK2: Brown colour)
(See Appendix D: Pg 13-17)
The 97 x 35mm roof rafters shown as brown rafters. These have been checked and
they do comply with current code requirements and the deflection of 3.77mm is within
the permitted deflection of 5.40mm
The deflection of the supporting truss (GT03) at mid span is 21.3mm (See Appendix
C.:Pg 53) The deflection of the double truss 2.5m from the front wall is (2.5 x 21.3)/4.8
= 11.1mm.
When the two are combined the deflection of the rafters will be 11.1 + 3.58= 14.62mm
which is beyond the permissible deflection of 5.40mm.
We do not know how the roof rafters are connected to the hip rafter.

ROOF RAFTER TO HIP RAFTER SPAN 1.3M
(See Appendix D: Pg 18-21)
This rafter when checked as an individual element deflects 2.90mm which is less than
the permitted deflection of 3.93mm and is therefore within code limits
The deflection of the supporting truss (GT03) at its centre deflects 21.3mm (See
Appendx C: Pg 52).
The lower chord of the truss TM35 is connected to GT03 and restrains the lateral
movement, but this restraint relies on how the lower chord is connected to the bottom
chord of the supporting truss GT03). We do not know how the two are connected.
And therefore at 1.8m from the front wall GT03 deflects (1.8 x 2.1)/4.8 = 7.98mm.
The combined deflection of the truss and the roof rafter is 2.90 + 7.98 = 10.88mm
which is greater than the permissible deflection of 3.93mm.

BASIS OF ASSESSMENT
(See Appendix B: Drg No. 220818-SK2)
The calculation of the deflection of the blue double truss GT03 are based on an
idealized triangular diagram idealized from the actual parabolic deflection diagram.
The maximum deflection of 21.3mm at the trusses mid-span has been taken from the
Calculation (See Appendix C Pg.52).
Note:
Pages 5-21 the roof and hip rafters have been designed in accordance with BS5268-
2 ‘The Structural Use of Timber’.
The shears analysis of the timber hip rafter is in accordance with EN 1993-1-8:2005.
The following loads have been used in the calculation.
• DL = 0.90Kn/m²
• LL = 0.75Kn/m²
• WL = 0.77Kn/m²
Our wind assessment gives a higherfigure of 1.06Kn/m². The wind loading has been
assessed using Ayreshire Design Tools (See Appenidx C: Pages A 1-4) this has been
applied the deflection of the roof rafters when the deflections of the roof rfaters when
combined with the proportional deflections of the supporting timber trus GT03, the roof
rafters fail in deflection.

PROBABLE CAUSE OF MOVEMENT
The cracking and movement at the corners of the house has been caused by either
one or a combination of the following:
• The deflection of the hip and roof rafters at the corner of the house and the
supporting double truss (GT03) ( See Appendix A).
• The lack of resistance by the brickwork at the corner of the house.
• The lack of a hip rafter and roof rafter restraint at the corner of the house.
• The underdesign of some of the roof rafters on the side elevation shown green
and brown.
• Inadequate lateral restraint for the wall plate at roof level.
• Failure in bearing on the supporting truss GT03.
• Inadequate joint design at the top of the hip rafter to the main truss.

In essence, the roof and our garage roof have both failed and will need to be replaced.

What this has meant for us

Because of the condition of the roof, we have been unable to insure our home, both building and contents insurance has been declined by our insurer and despite scouring many websites and reaching out to multiple insurance brokers (thank you all) no insurer will insure the buildings or contents of our home since June 2022.

The Impact and Disruption

In order to investigate the roof, the structural engineers required temporary boarding to be constructed in the attic. Bovis contractors were used to make our property safe whilst boarding out the attic, part of this was to remove the landing light fittings as they potentially would be damaged. It took the contractors 2 days to remove the light fitting and our pictures on the stairs and bulkhead and to board out the loft. After completing this they left us without power to the upstairs of our home meaning we were left to navigate in the dark. We were not made aware this would happen. The contractors stated this was because they had left live wires hanging from our ceiling, so turned the power off… another prime example of the standard of the health and safety from Bovis and their contractors!

The TimeFrames and Further Investigations

This roof investigation was initially booked in for 09/02/2023, however, the structural engineers didn’t arrive to inspect the roof until the week after, unnecessarily delaying the mess and disruption.

The report from the structural engineers was received on 18/04/2023 in an email from Bovis Customer Service director who stated: “I have today sent this to the suppliers of the trusses. They are going to speak to the software provider as the report appears to question the calculations outputted from the design software. I will write again when I have their findings in respect of the attached report as I think this will be relevant.”

After much chasing, I finally got a response to say that the manufacturers/designers wanted to inspect the roof, this inspection took place on 12/09/2023

Again after much chasing, we finally received the report from the inspection on 31/01/2024! 4 months after the inspection. This report contradicted the structural engineer’s findings and comment from the structural engineer is now required.

The reply from Bovis structural engineers was received on 28/03/2024. The excerpts from the report are below:

The rafters at the corners of the house are supported on a post bearing onto the wall plate detail shown on page 2 of the Report. See  Interpretation (Appendix B: Drg no. 220818-01-09). The roof and hip rafters should bear directly onto a wall plate bearing onto the inner skin of blockwork.

It appears that this timber post and elevated wall plate has been used locally to bring the internal leaf of the cavity wall upto the correct level.

The monopitch roof trusses and ‘loose ceiling joists’ have been nailed to the roof truss (GT03). The connection required a Cullen TM38 midi shoe (See Appendix C), this is a small joist hanger.

Roof bracing: This is not in accordance with Eurocode 6 PD6693-1-2019. Additional longitudinal bracing and sloping bracing is to be fitted (See Appendix A.

CALCULATIONS
(See Appendix A)

The calculations deal with the main roof truss and some loose roof rafters , calculations indicate that the hip rafters are underdesigned and they are contributing to the movement of the 4No. corners of the house.

(See Appendix A: Page 195, 199, 203, 211, 215, 246. Note: These are PDF Page reference numbers): The supports for a pinned joint (1) and a roller bearing joint at (2). The rafters at (2) are skew nailed and therefore a pin joint has been made. This will result in a horizontal load bearing applied at joint (1).

The diagram on Page 195 and the other pages listed above shows what we assume is a timber post bearing onto the wall plate.

The roof rafters should bear directly onto the wall plate. We do not know why this detail has been used.

End conditions for the end of the rafters connected to the hip rafter at the four corners of the building used in the calculations are incorrect. (these are referred to as loose timbers in the Report; See Appendix A).

HIP RAFTER

The support conditions shown are as follows:
2: Roller Bearing Joint.
a1: Pinned Joint.
a2: Roller Bearing Joint.

Due to the hip rafters being skew nailed on site, the actual end conditions are as follows:
2: Pinned Joint.
a1: Pinned Joint.
a2: Pinned Joint.

The design does not match the actual conditions on site, the 147 x 50mm TR26 hip rafter is underdesigned and contributes to the cracking at the four corners of the house. There should be no roller bearing joint (sliding bearing) end conditions.

CONCLUSION

The elevated wall plate detail contributes to the cracking noted at the 4No. corners of the house in the Report dated 07-10-2022.

This elevated wall plate should be braced and tied down with lateral restraint straps.

The structural design of the loose timbers (roof rafters) have used the wrong end condition at one of the supports. Where the roof rafter meets the hip or truss, a pinned joint should be used in the calculations not a roller bearing joint.

In essence, the roof design does not meet regulations and the roof has not been built to that design!

This took over a year of constant chasing for reports and replies to ascertain the entire roof needs to be replaced on both the house and garage.