Bricks and Framing

Old Buildings

Old buildings apparently have two stone walls with rubble and mud in between. Their structure would appear to be similar to old Scottish buildings. They have no damp proofing and water can ris through capiliary action.

There are plenty of books on caring for and renovating old houses, and on retrofitting them with insulation. Expect to use breathable plasters and renders, and compatible paints. It would seem tha a fair few old houses have been abused with modern materials and even modern wallpaper. One exception to the use of such products would appear to be capping the walls with a reinforced concrete ring beam.

Take care when purchasing an old building: we saw a lovely old house near Gois which had lost tiles. This had allowed water to wash out some of the mud, and seeds had blown in. A sapling was growing out of the top of the wall, and had displaced more tiles, which was accelerating the damage and the outer wall was dangerously bowed.

In the end we didn't buy an old house - or at least not an old stone one.

New Buildings

New house construction seems to be materially different in Portugal, compared to the UK.

The rules about seismic performance apply everywhere (even though the geology does not necessarily justify it) and loads are typically born through framing rather than load-bearing masonry. Some masonry systems provide for the columns to be formed in holes in the blocks themselves, so the blocks provide 'lost frmwork'.

Timber framing is not common.

Lightweight steel framing (LSF) has some traction.

There is almost no construction from what we would call 'SIPS', although you can get composite panels for prefab construction and roofing.

The majority of construction seems to use in-situ cast reinforced concrete frames with trench foundations, and builders seem to be pretty godd at it - or at least capable and competitive in pricing.

I understand that the concrete structures should have 4 lengths of rebar in a box structure and these are 100mm apart. They need 50mm of coverage by concrete so the structural pillars will be 200mm deep.

This Artebel block with pillar support can be bought with 200mm dpth, so perhaps the thickness of the block can count towards the covering of the rebar. Also (some) Ytong blocks can be bought with a 160mm circular hole for forming a reinforced column, although the blocks are 240mm or 300mm deep.

It would appear that the structural part of LSF can be thinner - perhaps down to 100mm. The steel forms a significant thermal bridge so while the frame can be filled with insulation, there is a good case for adding an ETICS system around it.

Houses that are new enough to be built with a concrete frame and infill blockwork:
  • may or may not have a cavity
  • may or may not have a damp-proof course
  • may or may not have any insulation under the floor

For buildings that had the project approved prior to 1992, there was no requirement to meet any standard of insulation: expect buildings built 'to standard' to have none.

Brick Wall Structures, for New Build

Take all this with a large pinch of salt and remember that I'm not an expert and this is worth what you paid for it, or perhaps slightly less.

I assume the presence of a reinforced concrete frame, and that the pillar thickness will be at least 200mm (rebar spaced at 10cm, with 5cm concrete protecting it).

So we have:
  • one layer of bricks, with external insulation (ETICS)
  • two layers of bricks, with a cavity that is lined against the inner wall with insulation and an air gap for ventilation and moisture control
  • two layers of bricks with the cavity completely filled

In the case where there is insulation in the cavity, then it does not seem to be completely standard practice to prevent thermal bridging where there are pillars. This is also the case with concrete platforms forming floors and roofs which extend outside the envelope to form balconies or shading.

The effect of thermal bridging (psi-values) of various arrangements of insulation at linear features like pillars, windows, floors and roofs can be found on this interactive tool.

Some insulation products have an open cell structure and may tend to wick water from a wet outer leaf to the inner leaf (hence causing damp) so it may be necessary to choose carefully if a fully-filed cavity is used. The procedure for creating a fully-filled cavity appears simpler, and (assuming dampness issues are avoided) it will provide a thinner wall.

The comparative thermal behaviour may be quite different if the cavity is ventilated enough to form a chimney effect: the thermal resistance of the external leaf and air gap is lost and in exchange the system will be more like a ventilated facade, which may provide better protection against direct insolation in summer.

It isn't clear to me whether products that are used in ETICS systems are all necessarily suitable for filled cavity use, since they may rely on the base glue coat to provide a vapour check and also rely on a more through final finish. A hygrophobic insulator, or one with an entirely closed cell structure (and careful joint treatment) should be OK. Additionally it seems advisable to use a breathable external render system.

From a simplistic point of view, using a fully filled cavity would appear to have a simpler and cheaper approach to fixing the insulation which may make it easier to contemplate using more insulation.

The ETICS fixing systems need:
  • base coat plaster/glue
  • mechanical fixings
  • sealing layer
  • mesh layer
  • additional coat on sealing layer
  • all this before the final render coat, and all as specified by the ETICS system vendor.
A partially filled cavity would seem to need:
  • insulation glued to the inner leaf
  • some mechanical fixings (?)
  • construction of drainage plane
  • careful construction of outer leaf to avoid snots etc causing bridges and/or fouling the drainage
A completely filled cavity would seem to need:
  • insulation temporarily supported against inner leaf (possibly glued)
  • outer leaf build against the insulation

There is a discussion on the Dow website about fixing the popular Wallmate CW-A with a ventilated double wall structure.

There is a wall structure illustration for EPS here which discusses condensation and vapour management.

There is a mention of using Isosfer Graphite Enhanced EPS on their web site - the JavaScript seems to malfunction currently. The image which it tries to display is here.

There are a number of technical sections showing ISOWALL use with and without an air gap. These illustrations appear to show the use of wall ties, while there is no mention in the others. Wall ties might significantly complicate installation, especially when using tijolo termico on the inside leaf since they seem to be a slightly different size to the tijolo traditional.

Many illustrations show a 3-hole block on the outside and a 2-hole block on the inside. I do not know if this is required - it would seem more sensible to have more thermal inertia inside, if the thermal bridge to a cold floor surface is managed. The psi-value calculator allows choice of 2-hole and 3-hole blocks but the wider block is outside: it also shows different psi-value effects for the fully- and partially-filled walls.

Insulation products for in-wall use seem to have a 'shelf' structure on their edges or a tongue-and-groove structure, as an aid to fixing to avoid air gaps. They also tend to be larger than the standard 1m by 0.5m blocks for external insulation, which are generally square-edged.

I have seen no mention of applying tapes to the board edges to help with air seal and moisture ingress along joints.

Bricks

Most structural bricks used are quite different to UK bricks. The nearest equivalent tpo the UK is probably 'tijolo macico' and these seemed to be designed for facing, paving, and sometimes for constructing ovens. The normal 'tijolo' bricks have large cavities that run horizontally along their length. There are more solid variations which are designed for insulation, with a focus that varies between acoustic and thermal insulation. However, these bricks are not used in load-bearing systems.

The mortar systems seem to be 'old school' thick bed systems, even when the blocks have a superficial resemblance to German Porotherm (or similar) blocks which use thin-bed systems.

The cost of ordinary tijolo is remarkably low. Even premium insulating blockwork is relatively inexpensive.

You can get prices from Artebel by registering on the web site. I'm not giving much away by saying that you will have trouble spending €30 a square metre of wall surface for bricks. Note that these insulating blocks are 'expanded clay aggregates' and Artebel (like others) seem to be licensees for Weber's Leca process.

You can also see pices on the Preceram page - for traditional bricks and also thermal ones. The thermal and acoustic blocks look like German ones but they are much cheaper - and apparently not made to anything like the same precision. Be amazed that you can fill a metre-square hole with standard tijolo 22cm deep and pay just €4 for them (plus labur and mortar). Even the deepest thermal bricks will be less than €10 a square metre unless you live a long way from the factory. There seems to be concern that the quality is not high, and that many bricks are mis-shapen or out of (generous) size limits.

See also Prelis who make standard bricks, thermal bricks and bricks with column formwork. They also make an interesting brick with tongua and groove system called tijolo Unoko: the tongue and groove verticals are more commonly seen on thermal bricks.

A further thermal block provider is Zenith at presdouro who make thermal blocks in a variety of sizes. Presdouro also sell lintel and column blocks for lost formwork and the 'thermal paper' blocks to place outside them.

See also Pavimir.

And Pavineiva.

You can get Ytong blocks in Portugal with local support, but they are made in Belgium and the transport is expensive.

The Isoltermix blocks from look interesting to me. The depth of insulation is broadly in line with the calculated optimum here and they have a U-value of 0.36. The (uninstalled) cost is broadly the same as two layers of thermal blocks from Artebel or Preceram plus some insulation - it's less than €30 per square metre of wall. Given that placing the blocks should be less labour-intensive than placing either a single block layer and an ETICS system or placing a double wall with insulation in the cavity, then these blocks would appear to be something of a bargain providing the target U value is what you want. They also provide 'lost formwork' and the pillar construction should be cheaper - and result in less delay - as a result.

I have some minor reservations regarding:
  • thermal bridging between 'outside' columns and 'inside' columns at a ring beam and base beam
  • establishing air tightness

The residual bridging will need some thought (not least because it might be a relatively minor effect) and air tightness might have to be addressed by careful rendering - it may mean that a slightly more expensive render solution is necessary.

A similar block is made by ACC. It has slightly higher claimed performance but does not seem to be matched by a lost formwork system. ACC make lost formwork, but it is necessary to add the thermal shield afterwards. These 'extra' blocks allgedly have 8cm of insulation and are about €3.50 each for a U value of 0.28. The discussion suggests a base wall cost of about €40/m2 and a finished cost of about €60. Video. If a 20cm concrete frame already exists, they would appear to be an excellent approach.

Reinforced Concrete Framing

This seems to be the standard construction technique by default. That is likely to mean that:
  • it will be easier to get ingineering calculations accepted by the Camara
  • it will be easier to get competitive quotes from builders
  • estimates and timescales will be more accurate
The framing typically extends:
  • from strip foundations (including support for internal walls)
  • concrete floor structures
  • verandas and balconies, often extended directly from the adjacent floor with no thermal break
  • concrete roof structures particularly on flat roofs)
  • shading structures over balconies, often extended directly from the adjacent roof with no thermal break
If you set aside 'eco' concerns about concrete, then the generic structure would seem to be a mixed bag thermally:
  • the mass available would be attractive to provide thermal inertia to protect against overheating
  • the cold bridging (especially to balconies etc) will require thermal treatment of external elements or may lead to cold spots that can attract condensation

It may be possible to be overly concerned about thermal bridging, but retrofitting an existing frame and floor structure to be anything like Passivhaus will be very difficult - Passivhaus expressly considers addressing thermal bridges, because they will dominate if they are left untreated and planar insulation and air replacement is very effective.

Note that while some insulation elements claim high compressive strength, the strength is suitable for carrying columns of bricks but not for insertion in the base of a column, which must carry its own weight and that of a portion of the roof structure.

Rebar

I have no idea if you can get (or are allowed to use) unusual rebar systems in Portugal.

I need somewhere to pin the links however, so:

Light Steel Frame

Knauf Aquapanel:

The video is interesting - as is the claimed performance. I'm not sure how the U value can be so good, with the steel sections causing cold-bridging.