Dennis-Wild Steel Framed House - Non Traditional Construction
Manufacturer: James Wild & Co (Housing)
Period built: 1920s
Number built: 10,000
Alternative names: Dennis, Dennis Steel Frame House, Dennis-Wild Patent Steel Frame, Composite System, James Wild, Wild, Wild Steel Frame System.
Dennis Wild Steel Framed House.
Shortly after the first World War of 1914/18, a number of committees were set up by the British government to examine the construction industry and to report on ways of solving the acute housing shortage and the severe lack of skilled labour and building materials.
The 1919,Standardisation and New Methods of Construction Committee, invited suggestions from the public for novel methods for building houses.
The committee received a large response to the invitationa, resulting in a new list of approved methods for construction being published, which covered the Committee’s work up to the period of April 1920. The Committee finally ceased to function in 1921.
The method of construction used in the Dennis-Wild system is not featured in the original 1920’s list of approved construction methods but due to the fact that over 100 Dennis-Wild houses had been approved for construction in Blackpool during 1922, it is considered highly likely that Committee provided and approved this development.
Interestingly, the Burt Committee of 1942, lists two different sponsors for this building system. The first being, James Wild & Co (Housing) Ltd of Blackpool as the sponsor of the Dennis-Wild system and Edgar B Dennis, also of Blackpool which is listed as sponsor for the Dennis system, which according to the description provided,appears remarkably similar to the Dennis-Wild System.
No date is listed for the Dennis system, and no further mention of Edgar B Dennis can be found. It is possible that these two seperate sponsors may have merged to support the one single system that we know today as the Dennis -Wild system.
Copies of drawings from the period 1925/29 show the system as:-
During the 1920s approximately 9,000 Dennis-Wild type houses were built on various sites in England with further undocumented numbers also being constructed in Scotland and Wales.
Externally, the Dennis-Wild house appears at first glance to be of traditional construction typical of the period. There is no clear indication that the structure conceals a steel frame.
The two storey dwellings range from semi-detached blocks to terraces of up to six dwellings, the terraces having ginnel access to the rear gardens.
All of the roofs seen have hipped ends. On plan some semi-detached blocks are rectangular in shape, whilst others have bay windows on the ground floor and sometimes have projecting extensions on the flank end. The terraces can be either rectangular in shape or have the end dwellings turned through 90 degrees with the front elevation projecting beyond the line of the block, but with a common face along the rear elevation.
There is a variety of external finishes. Most have facing brickwork up to first floor level, usually finished with a projecting band course. From
the first floor to the eaves the walls are either tile or slate hung or are rendered and pebble-dashed. Alternatively the walls may be of facing brickwork from ground to eaves level sometimes with decorative inband and outband quoins in facing brickwork and common brickwork infilling (Figure 1).
Internally, on the ground floor, the rolled steel stanchions in the middle of the front and rear elevations may protrude from the line of the wall, in which case the stanchions are likely to be encased in either concrete or plaster. The stanchions on the line of the separating wall and the flank end wall are not always visible.
The main floor support spans horizontally between the middle stanchions in the front and rear elevations. This support projects below the ceiling level and is commonly encased in timber. The floor support channels which run along the line of the separating wall and the flank end wall are not always visible.
In situations where the second storey has rendered coating or hung tiles, the walls to the storey may be of thinner construction and the internal projection of the stanchions is likely to be more prominent and these too were also commonly encased in timber.
At eaves level, a small area of the ceiling around the perimeter is sloping; the bottom of the hip rafters and the main roof truss protrude below the slope and are sometimes also encased in timber with a decorative beaded edge.
Since it is possible that none of the stanchions will be plainly visible, the only sure indication of a Dennis-Wild house is the presence of the
patented, and unmistakable, Cradle Roof Truss (Figure 2a, b), which is completely unique to this system.
The typical frame components for one house in a semi-detached pair are:-
Seven Eaves height “I” section rolled steel stanchions.
One Single storey height “I” section rolled steel stanchion.
One “I” section rolled steel first floor support beam.
Two Channel section rolled steel first floor support beams.
Three Angle section rolled steel ties at first floor level.
Cleats and support plates were rivet ted to the steelwork in the factory and connections made on site are bolted (Table 2 lists the sizes of the
The typical frame (Figure 4) has three eaves height stanchions in both the front and rear elevations, one located at each flank end corner (A1 or A3), another at about mid-point along both walls (81 or 83), and one on the line of the separating wall (C1 or C3), which is shared between adjacent properties. A further eaves height stanchion (A2) is located at about mid-point along the flank end wall.
At first floor level the stanchions are connected by two floor support channels, a main floor support beam and two angle ties. The floor support channels (E1 and E3) connect the stanchions A1, A2 and A3 along the flank end wall and the stanchions C1 and C3 along the line of the separating wall.
The main floor support beam (E2) spans between the mid-point stanchions 81 and 83 in the front and rear elevations, and is Pl’ “”ped at about mid-span by,” ‘J””,;le storey stanchion (82).
Angle ties (01 and 03) connect the stanchions A1, 81 and C1 in the front elevation and the stanchions D3, 83 and C3 in the rear elevation.
A lighter section angle tie (D2) spans from the flank end wall to the separating wall over the tops of the floor supports; the location of this
angle tie is not precise and it may only have served to stabilise the framework whilst other connections were made. (Figure 5 illustrates some
A timber beam typically 5 ins x 3 ins is connected to the stanchions around the perimeter at first floor level and acts as a sole plate for the
studwork in the upper storey.
A similar timber beam spanning over the tops of the stanchions, provides the only connection between the stanchions at the eaves and also acts as a head plate for the studwork and a wallplate for the roof construction.
Vertical timber studs are fixed between the two beams at regular intervals.
(Sizes of these timber components are given at the end of Table 2).
2.4 External Walls
The external walls are of cavity construction up to the first floor level.
The outer leaf is of 4 ~ ins brickwork usually finishing with a projecting band course, and the inner leaf is of 3 ins blockwork. (Table 3).
From the first floor to the eaves the external wall is tile or slate hung on battens fixed to the timber studwork. The inner leaf is of 2 ins blockwork built off the first floor boarding and nailed to the inner face of the timber studwork.
The internal finishing is of sand/lime/cement backing coat and a plaster finishing coat.
2.5 Separating Wall
The separating wall is usually of cavity construction with two leaves of 3 ins blockwork with a 2 ins cavity between (Table 3).
On the ground floor the partitions are typically of 4 ~ ins brickwork and 2 ins blockwork. On the first floor the partitions are of 2 ins blockwork throughout (Table 3).
2.7.1 Ground Floor
The ground floor to the living area of the house is of suspended timber construction, with 4 ins x 2 ins joists at about 15 ins centres spanning
from the front elevation towards the rear elevation and supported on honeycombe dwarf walls. The floor to the kitchen area is of solid
concrete. (Table 3).
2.7.2 First Floor
The first floor is commonly of 6 ins x 2 ins timber joists at about 16 ins centres and span from the flank end wall to the separating wall. They are supported on the steel channels at the flank end and separating walls and on the main floor support beam at about mid-span. (Table 3).
The ceilings are usually of lath and plaster throughout.
The hipped roof is largely conventional in construction, except for the single James Wild Patent Cradle Roof Truss. The unique feature of this
truss is the use of steel rods to support the strut below the purlins, avoiding the need for a load bearing wall below (Figure 2a).
The roof truss was designed to be assembled on site from pre-cut timber and steel bracing rods, and bolted to the top of the mid-point stanchions in the front and rear elevations.
The substantial timber members used for the two rafter elements of the truss are notched on the underside to fit over the purlin, which is also notched. A strut, morticed to the purlin to prevent slipping, is located below the cross over point and supported at the foot in a half round steel shoe. Pairs of horizontal and diagonal steel rods connected to the steel shoe are used to brace the truss.
The rest of the roof is constructed with hip and common rafters in a conventional manner using the timber eaves perimeter beam as a wallplate.
The differing external treatment to the elevation of the upper floors has already been mentioned. The position of the frame within the external envelope varies from site to site, in some instances the frame is buried within the thickness of the wall and in others it projects from the face of the inner leaf, usually encased in either concrete, plaster or timber.
However, the basic arrangement of stanchions, channels, angles and beams is similar for all sites.
Variations seen were:-
Rolled steel angles used as corner stanchions instead of “I” section rolled steel stanchions.
All of the stanchions in the external wall totally encased in concrete up to first floor level.
An additional rolled steel beam at first floor level spanning from the flank wall to the separating wall and crossing below the main floor
Single storey stanchions (C1 and C3, Figure 4) in the junction of the separating wall, and (A2) in the middle of the flank wall, with
substantial timber studs bolted to the head plate of the stanchions and connected to the timber eaves perimeter beam in place of eaves
height steel stanchions.
In cases where the end of terrace property is turned through 90 degrees, the front elevation projects beyond the line of the block and
an additional eaves height stanchion (C2 Figure 4) is located at the junction with the adjoining property.
An additional single storey stanchion (C2, Figure 4) in the middle of the separating wall propping the floor support channels. Typically
these floor support channels are built into the brickwork of the central chimney breast.
A truncated cradle roof truss with the apex trimmed to a horizontal cross piece to allow the hip rafters to pass over or notch into the
top (Figure 2b).
Rendered and pebble-dashed external finish to the upper storey on either:
3 ins blockwork nailed directly back to the timber studs or alternatively secured with butterfly type wall ties nailed to the timber studwork:
Or on 3 ins blockwork or brickwork on edge cavity construction.
Absence of the timber perimeter beam at first floor level and the timber stud work to the upper storey.
Facing brickwork outer leaf from ground to eaves level, sometimes with decorative quoins.
Brickwork on edge inner leaf, partitions and separating wall.
Two storey flats with entirely rendered walls.
Plasterboard dry linings to the external walls of the upper storey fixed directly to the timber studwork.
Other variations in construction and layout are known to exist, details are uncertain but the construction is thought to be substantially as described.
2.11 Corrosion Protection
At the oldest site visited it was apparent that no protective coating had been applied to the steelwork. At the seven other sites traces of a
protective coating were visible.
A sample of the coating from one site was taken for analysis and proved to be a red lead primer. An earlier report (Reference 2) mentions red oxide as a likely coating.
3 PERFORMANCE IN USE
Surface corrosion of the steel frame is apparent on all of the houses examined, but severe corrosion with some loss of section has been limited to the lower parts of the stanchions and less frequently around the lateral connections at first floor level.
Almost all of the instances of severe corrosion have been observed in corner stanchions; however, proportionately more of these stanchions were exposed by the investigators since there is a greater chance of one of the faces being subject to driving rain.
Although on one site severe corrosion was seen at the foot of the stanchion buried in the middle of the separating wall (Stanchion C2, Figure 6c).
These findings confirm the results of the earlier investigation of Dennis-Wild houses (Reference 4).
3.1.2 Corrosion of the Structural Frame
(a) At four of the sites severe corrosion of the bottom section of
some of the rolled steel stanchions was seen. This ranged from
rust scale sufficient to reduce significantly the thickness of the
metal section, to perforation of the flange of the stanchion
(Figure 6 a, b, c, d, e).
(b) On the four other sites moderate corrosion (2 to 3 mm thick of
corrosion product) was seen at the foot of the stanchions.
(c) On one site a prior survey carried out by the Local Authority revealed severe corrosion to stanchions at first floor level and to one corner stanchion up to eaves level.
(d) Minor corrosion (less than 2 mm of corrosion product) was seen on all of the sites, and on all of the sites the initial protective coating (when applied) had been largely breached.
3.1.3 Deterioration of the Timber Components
(a) On one site severe decay was evident in the timber perimeter beam at first floor level (Figure 7). The timbers appeared to be in sound condition on all of the other sites where examination was possible.
This problem was also noted during a controlled demolition carried out by one of the Local Authorities.
(b) Long and unequal spans in the roof purlins of one layout has led to bowing of the timbers and subsequently to the tilting outwards
of the roof wall plates.
3.1.4 Deterioration of the External Components
(a) Vertical cracks in the brickwork up to first floor level are common, usually coinciding with stanchion locations.
(b) Bulging of the brick walls on both the rear elevation and flank ends.
At one site this problem was particularly severe, and evidenced by the band course at first floor level tilting outwards.
This problem has probably been aggravated by the performance of the wall ties (See (e) below).
(c) Vertical cracks are often present in the pebble-dashed rendering to the walls of the upper storey, coinciding with the studwork; these are probably caused by differential movement and to the practice of nailing the blockwork back to the studs. Spalling of the pebble-dashed rendering from a brickwork substrate was also noted.
(d) Tile and slate hanging to the walls of the upper storey has deteriorated or become damaged; lack of a waterproof barrier behind the tile hanging has led to rain penetration and the risk of rot in the timbers (See 3.1 .3a above).
(e) In some houses there were insufficient wall ties, or wall ties not effectively bridging the wide cavity, or corrosion of the wall ties bedded in black-ash mortar, or wall ties sloping inwards owing to coursing problems with the brick on edge inner leaf.
(f) Some deterioration of the briCkwork surfaces, particularly below DPe level, probably caused by frost damage.
4 GUIDANCE ON INSPECTION
Section 3 is a compendium of deterioration and faults that have been reported to or identified by BRE which are specific to the Denni-Wild steel framed house.
The principal defects are:-
Corrosion of the stanchions at the bottom (3.1.2 a, b, d).
Corrosion of the stanchions at first floor level and up to eaves level
Rot in the timber perimeter beam at first floor level (3.1.3 a).
Bowing of the roof purlins and tilting of the roof wall plates
Cracks in the brickwork at stanchion locations (3.1.4 a).
Bulging of the external walls (3.1.4 b).
Spalling and cracks in the pebble-dashed rendering to the upper storey
Deterioration of and damage to the tiles or slates used in the
vertical tile hanging (3.1.4 d).
Insufficient numbers of wall ties, ties not effectively bridging the wide cavity, ties sloping inwards, and corrosion of the ties particularly where bedded in black-ash mortar (3.1.4 e).
Frost damage to the brickwork surfaces (3.1.4 f).
These do not constitute a comprehensive list of possible defects. Equally not all the above defects will necessarily be present in one property.
Nonetheless this list serves to highlight features which should be subjected to close examination as part of any overall inspection procedure
for Dennis-Wild houses.
It is emphasised that if significant corrosion of the steelwork has occurred, the extent of deterioration may be masked by the corrosion
product itself. In such cases it is difficult, if not impossible, to determine the condition of the steelwork solely by visual means. This
limits the effective application of purely visual inspection techniques, including the use of optical probes such as borescopes. If corrosion is
seen to exist, the component should be exposed in order to enable the extent of deterioration to be determined by removal of the corrosion
5 GENERAL COMMENT ON CONDITION
The observations in this report result from examination of Dennis-Wild houses in England, Scotland and Wales.
Some of the houses were in their original condition, others had been or were in the process of being refurbished.
The extent of deterioration varied from house-to-house and from site-to-site. Serious deterioration of the steel frame has been identified
on a number of the sites and as the extent and significance of the deterioration varies, it is advisable that each house be individually examined.
As with all steel framed houses, repairs to the frame are straightforward in principle. Affected members can be cut out and replaced by new
steelwork adequately protected against corrosion. (Reference 5)
This report was prepared as part of the research programme of the Building Research Establishment and is published by the permission of the Director.
This report was prepared by E Grant, based on site studies and other work carried out by J R Britten, R N Cox, A Christie, P Finch, E Grant,
K C Harling, H W Harrison and J Thompson.
The ready co-operation of the Local Authorities who made properties available for inspection and provided copies of their own structural
surveys is much appreciated.
The Dennis-Wild House was typically built as 2-storey semi-detached and terraced houses.
These properties typically have a medium pitch hipped roof that is covered with either tile or slate. The external walls are constructed using standard brick but surface design does vary, often with a split in material usage between the upper and lower elevations. Whilst brick is typically exposed at the lower elevation, the upper elevation may be rendered, pebbledashed or hold hanging tiles including slate above, some may even be brick up to eaves level.
Some of these houses also have single storey bay windows at the front elevation. The roof will typically have a Cradle roof truss incorporating iron tie rods.
The BRE lists the following notes to Surveyors who should check for:
Moderate to severe corrosion of RSJ stanchions has been noted. Corrosion can be particularly at stanchion bases.
Damp proof Course is not always present.
Vertical cracking of brickwork can sometimes be found where stanchions are located.
Vertical cracking has been noted in the upper floor render, particularly at the timber stud locations.
Bulging of external walls may be present.
Wall ties: Can be insufficient, failure to bridge wide cavity, may also suffer from corrosion.
Decay of timber perimeter beams at first floor level has been found.
Bowing of timber purlins and tilting of timber wall plates has been noted.
This system was also used to produce flats.