Structural Engineers Report

Transcription

1 Consulting Civil and Structural Engineers 68D Swan Yard King Street Norwich NR1 1PG Tel Fax Structural Engineers Report For Brown & Co Old Bank of England Court Queen Street Norwich NR2 4TA Regarding Bergh Apton Hall Barn Bergh Apton Norwich Norfolk 10 May 2007

2 Consulting Civil and Structural Engineers 68D Swan Yard King Street Norwich NR1 1PG Tel Fax Our Ref: DJQ/MJB/1449 Date: 10 May 2007 Your Ref: KJS/DNHH/7210/JY For the attention of Keith Sewell Esq Brown & Co Old Bank of England Court Queen Street Norwich NR2 4TA Dear Sirs Re: Bergh Apton Hall Barn, Bergh Apton Freeman Executors We refer to your recent kind instructions, for which we thank you, and having visited the above property to carry out certain investigations, now submit the following report. We understand the extent of your instructions to be to carry out a structural assessment of the barn to give a general structural overview and more specifically with regard to it s conversion to a habitable living space. The content of this report is thus so confined. We have not inspected the woodwork, or other parts of the structure which are covered, unexposed or inaccessible, and we are therefore unable to report that any such part of the structure is free from defect. Cont

3 Page 3 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 1.0 Description of Premises 1.1 Briefly, the barn comprises a timber framed structure with the walls built off a masonry plinth approximately 600 mm high around the perimeter of the building. The walls above the plinth consist of timber studs and shiplap boarding. The roof is relatively steep at around 45 to 50 degrees and is currently clad in corrugated sheeting. Support to the roof is provided by a number of principal trusses which generally take a collar and tie formation, although the collar and tie do not always occur on the same rafter. The principal trusses carry purlins which in turn support the common rafters. Generally the roof trusses are carried on vertical posts down to wall plate level, with a knee brace at the eaves junction. 1.2 The barn comprises one of a series of agricultural buildings in the immediate vicinity. These are of varying materials and constructions. 1.3 The site is gently sloping and surrounded generally by farmland and woodland. 1.4 The age of the property is not known, we estimate however that it is at least 100 years old and probably significantly older. 1.5 Given its past usage, whilst surface water drainage was noted by the presence of gutters and down pipes no foul drainage system is anticipated.

4 Page 4 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 2.0 Description of Defects 2.1 The defect in respect of which our advice has been sought is to comment upon the general condition of the barn in respect of its structural robustness as well as its economic viability into converting the building for domestic use. The content of this report is thus so confined. 2.2 The agents acting on behalf of the applicant have produced survey drawings. It is our understanding that Architect s proposals are currently being prepared.

5 Page 5 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 3.0 Investigations: 3.1 An exploratory trial hole was not considered necessary since given our local knowledge of such properties, together with their known date, the most likely foundation would be a nominal brick outstand constructed between 150 and 300 mm below ground level. 3.2 At the time of our visit, a visual inspection was carried out and a series of photographs, which are appended to this report, were taken with their descriptions being set out below. Photograph Nos inclusive show the external elevations around the property, indicating the timber clad main barn structure and corrugated sheeting to the roof. Photograph No. 11 highlights the presence of guttering and downpipe to the west elevation, showing also missing cladding boards. This elevation was generally inaccessible due to overgrowth of vegetation. Photograph No. 12 indicates the broken lintel over the main entrance to the barn. Photograph No. 13 further showing missing cladding to the west elevation. The plinth beneath the post adjacent to the opening is collapsed locally, requiring repair. Photograph No. 14 indicates cracked blockwork to the plinth. Photograph No. 15 shows insect damage to a timber stud as part of the external wall. Photograph No. 16 is an interior elevation on the north gable wall showing the generally sound construction. The collar and tie principal trusses can be seen in addition to the knee braces and diagonal wind bracing to the gable wall. Photograph Nos. 17 & 18 show details of the eaves and general roof construction including double purlins and common rafters. Note the steel tie rods inserted through the wall plate at eaves level.

6 Page 6 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co Photograph No. 19 highlights the valley to the main roof from inside. Generally the roof is reasonably sound, however a damaged timber beam is visible to the right of the picture. The dowelled splice joint has failed and an acrow prop has been installed to prevent further damage. Photograph Nos. 20 & 21 show further details of the damaged timber beam over the opening into the rear of the barn. Photograph No. 22 shows the internal elevation on the eastern gable wall to the rear of the barn. Again indicating the generally sound condition of the timber frame. Photograph No. 23 shows the internal elevation on the southern gable wall. Whilst the walls are missing areas of cladding, the sound condition of the original timber frame is clearly in evidence. Photograph Nos. 24 & 25 these are taken looking up into the roof. Daylight can be seen which will let in rainwater and ultimately could damage the timber frame. Photograph No. 26 shows a view looking east to west. Photograph No. 27 highlights the broken lintel over the main entrance. Photograph Nos. 28 & 29 indicate a missing section of the brick plinth internally which requires repair. Photograph Nos. 30 & 31 show the extent of the attractive original timber framework Photograph Nos inclusive detail damage to the timber wall plate and brick plinth on the western elevation due to water ingress and general disrepair.

7 Page 7 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 4.0 Discussion 4.1 The timber frame appears to have been largely untouched since construction and as such retains much of its original character. Generally the frame appears reasonably sound although evidently piecemeal repairs have been carried out at various times to small areas of the building, whilst other areas have obviously suffered at the hands of time. 4.2 Some areas of the external cladding are missing (photograph nos. 11 & 13), predominantly to the southern and western faces of the building which has allowed the ingress of both water and vegetation. An obvious result of this is both the growth of mosses etc on the timber wall plate on these elevations, in addition to several sections of wall plate and timber studwork which are badly rotted (photograph nos. 33 & 34). Left unattended this situation will only worsen. 4.3 In addition to the rot mentioned above, sections of the timber wall plate and a number of the timber studs forming the external walls have been attacked by insects (photograph no. 15) and some sections will require treatment or possibly replacement by skilled craftsmen to ensure that the original character is retained. 4.4 The roof, whilst generally appearing sound, does show daylight through a number of small openings which will allow penetration of rainwater. Over time this may have serious consequences for the internal timber frame. 4.5 The masonry plinth is in a poor condition in places and in some locations will need to be repaired or re-instated (photograph nos. 28 & 35). Cracking is evident to a portion of the plinth which has been re-built in blockwork (photograph no. 14). This would appear to indicate some degree of structural movement in the past, which is not surprising in a structure of this type.

8 Page 8 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 4.6 The timber lintels over the main opening into the barn and to the opening into the rear portion of the barn have both split and badly deflected (photograph nos. 12, 20, 21, 22 & 27). This appears to be due to overstressing of the timber rather than weakening due to insect attack or rot. As a result of this, the ridge of the roof has sagged in a corresponding position (photograph no. 3). The lintel to the rear is currently supported on an acrow prop (photograph nos. 21 & 22). 4.7 Whilst the effectiveness of the roof drainage is not known, it can be seen that the guttering over the main entrance is displaced due to the damaged lintel. It is most likely that large amounts of water will spill onto the ground at this point, creating problems associated with saturation of the adjacent soil such as foundation movement, in addition to the obvious problems associated with concentrations of damp as discussed previously. 4.8 As stated previously, a number of the structural timbers throughout the building show signs of rot and insect attack and as such will require treatment to prevent further damage, and in severe cases replacement. It should be noted that the structural integrity of the timber frame has been compromised by this attack and additional loading would not be advised on the existing frame. Should it be proposed to tile the roof then careful consideration will need to be given to carrying the additional load that this would place on the structure. 4.9 Considering the conversion of the barn there is sufficient space to allow for an intermediate floor in order to provide first floor accommodation. It would therefore be our recommendation that an independent timber frame, constructed in sympathetic materials and style, is utilised to support a new first floor construction. This independent frame could then be used to provide a stable platform to introduce lateral restraint and enhance the stability and robustness of the existing structure. This would be not only beneficial to the structure as a whole but would have the added advantage of placing any further loading onto new foundations, leaving the existing frame to enjoy its senior years in relative comfort As stated previously, the existing foundations are in all probability constructed with shallow brick outstands.

9 Page 9 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 4.11 The foundations in this case are relatively modest by current standards given the ground conditions encountered are for a clay subsoil which can be problematic. Clay soils have the property of volumetric change when changes in the moisture content occur. Reduction in moisture content produces shrinkage of the soil. When moisture content is taken up subsequently, then the soil expands, and this process is defined as heave. Therefore, any foundation formed in such soils will consequently experience movement, with this movement being generally reflected in the construction above. Reduction in equilibrium moisture content in such soils can be induced by natural climatic change, such as periods of drought, or induced by root action of trees and shrubs. Not all clay soils exhibit the same amount of volumetric change and the amount will be dependent, also, on whether the soil is a pure clay, or a mixture of clay and other soils, such as sand, which do not exhibit such properties. The degree of volumetric change which can be induced by trees and shrubs is dependent upon the species of tree, together with its proximity to the foundation. Each circumstance is individual and a bespoke design, and it is therefore normal practice to refer to the NHBC standards and guidance. In the absence of trees or shrubs, the foundations still require being formed at a greater depth than would be the case on sands and gravel s, in order that they should not be at a depth below the depth which normal desiccation can occur during periods of drought. Current interpretation of Part A to the Building Regulations is such that the foundation should be founded not less than 0.75 m below ground level However, at the time of our visit to the property there was little evidence to suggest the barn was suffering unduly as a result of shallow foundations. In the circumstances, we do not consider the need to enhance the existing foundations by underpinning and we would not expect any further movement due to initial building settlement given the passage of time and that domestic floor loadings are considerably less than agricultural. Thus, providing suitable drainage for both foul and surface water is introduced and advice with regards to planting of trees in proximity to buildings in clay foundations is observed in accordance with Chapter 4.2 of the NHBC recommendations, we have no further comments to make In addition, an adequate foul and surface water solution will need to be derived but this is all considered to be within normal building practice and not prohibitive.

10 Page 10 / continuation/ DJQ/MJB/1449/ 10/5/07/ Brown & Co 4.14 It has been within our wide experience that a sympathetic approach for a conversion of the barn into residential occupancy will give an opportunity to enhance the structural robustness and integrity of the barn without destroying the character of the property or its visual impact on the surrounding area Further, this window of opportunity would eliminate any out of character adornments such as mismatched brickwork and therefore considerably enhance and extend the useful life of the barn, without widespread renewal or replacement of structural elements Whilst outside the scope of this report, we consider it worth noting that the architectural scheme will need to satisfy Part L of the current Building Regulations in terms of insulation and thermal performance Overall, renovation of this barn provides the opportunity for the restoration and retention of a fine timber framed barn in an attractive location. Whilst the building is not without its defects, we would consider that sympathetic repairs coupled with the addition of a new independent structural frame would provide an economically viable method of providing a habitable living area within the existing space. We submit this Report to you at the present time, and for any further instructions you may have for us in this regard. Yours faithfully David J Quantrill BEng On behalf of The Burrell Partnership John R Illingworth CEng, MIStructE On behalf of The Burrell Partnership

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