ruggers

@Dave JonesThanks Dave, whats the difference with the marmox blocks and a celcon/aircrete/thermalite block for the first course? I was going to run a course of them round before I build my inner walls with normal block on top. The marmox looks very expensive. I had a look at EPS and I'd need 240mm to equate to 160/165mm PIR. The saving was £700 but by the time I'v bought the extra course of bricks and paid the labour it just works out the same.

@Canski *on quotes just delete the text unwanted and then tap enter twice at the ned of the sentence to split paragraphs* It's always good to hear from experience. It does sound a bit of a pain if the tolerances of the PIR are out. For the price you pay a tenner a sheet and £4500 quid later it should be machines to size. My joists are going on internal masonry hangers. Door and window reveals say they need a wall tie every 225mm so they'll need slit to. I won't be able to use a PC lintel over the external vent because it's all facing bricks otherwise I would.

I was looking at the boards and imagine the tongue at the top and one side adds the small over size but just needs slit into by the wall tie to make the T&G meet tightly together rather than square edge that neatly slips between but then has all the problems of the gaps if incorrectly fitted or a bit of wind gets at them while building. There will be 100 PIR and 50mm cavity spare, 350mm in total so I think 275mm wall ties are the correct ones, need to check the drip loop in the middle is away from the 100mm board. Yes good point, I was thinking of this, I was planning on fitting the vents the same way, it will mean they probably can't be spaced equally from outside, it will just be a case of finding gaps between the beams that align with the brick bond outer wall and within the maximum recommended spacings. I was thinking to build the infill mix up to the top of the first brick on the inner leaf which would be just under the telescopic vent, then we'll have to infill before fitting the vents to the slip coarse. It depends on how high it needs filled to provide support. I'm sure I seen it needs to have a 150mm gap to the underside of the insulation which would work out well. (So lower than my last sketch)

I think if the founds are decent the builders happy to use trench blocks for the first course, I've had a few mistakes with my plans so just trying to get the last part right. I'm not sure how much building control hold you to the plans for below DPC. They've already passed them, we are just changing to suspended beam for heave reasons. If taking the insulation down another block course was beneficial for cold bridging I would but if its so minimal I'd rather spend my time and money in other areas are all to a good standard. Thanks & I will be posting some progress up for others in the near future.

I appreciate what you've said but I've covered this before and I'm due to start in 2 months. Can't use EPS bead we are in exposed weather zone 5 face brick exterior so it's no good. It would be a nightmare to get passed by anyone locally because it's not used, everyones either timber frame or partial fill where we live and behind the times on anything new like weather comp or heat pumps within 70 miles. I agree the blown bead would be a winner and easier. I'm paying extra and using tongue and grooved 100mm PIR to save the hassle of taping the joints and it not sticking in bad weather or people just skipping it. We've had to do a last minute change from slab to beam and block and everyones been very slow compared to other peoples services used so I daren't make a single change bar getting this below DPC agreed. 2 years to get some plans sorted is too long. I just want to get on with it now and be done with changes but I have this last bit to finalise.

Slight edit to the original post sketch. The height of the lean cavity infill can be lowered to suit. Builder doesn't like to run the first course in trench blocks, something to do with them not being as easy to cut and level up if the founds arent level. The first inner leaf block on top of the beam and block floor will be an aircrete type like my last post. My question is, I'd like to know if the cavity wall insulation is fine as it is or has to go down abother 225mm? I cant see any benefit to it being lower down. The screed has insulation under it, the vented void will always be cold air, the inner leaf has the insulated block on it. The way drawn works out well for pallets of xtratherm tongue and groove pallet orders, if i go deeper its into another £1500 pallet so I'd have to do the base coarse in stocked square edge or xps.

Thanks, I'll just stick with the staffs I think, that was my original choice in smooth until offered the ones in the original post. You know they've been tried and tested.

@Johnny Jekyll thanks for the info. I don't see an insulated room built around the MVHR unit in a cold loft being much different to a warm loft if the roofs insulated too, so I can only assume the ducts must be affected the greatest from this unless, it's the surrounding temperature of the remaining cold loft design would affect the room built within it.

I agree with what your saying but I think in a cold loft, well insulated ducting would manage ok in winter especially with 400mm of mineral wool over it as Johnny is is doing, but summer would become the issue as the tiles/slate heats up from solar gain, it then warms everything with it and if the heat can reach the ducting, your going to get hot air blowing into the rooms even in summer bypass mode. If the unit manifolds and ducts can't all be within the thermal envelope, there has to be a trade off, so to minimise that It's important to keep loft duct runs as short as possible, and individually lag them. Some companies say the loft insulation over the ducts is enough and it certainly isn't. Adding some roof vents and gable end vents will help in summer to add cross ventilation but it's probably never going to be enough. It will certainly help move some of that hot air though. Have you tried contacting some reputable installer companies and asking this question, the two I've spoken to will answer this for you. Even if you add them to the walls but have to do the ceiling vents for the bathroom and ensuite if it's best, it's a small trade off in not doing all of them this way?

Hi, interested to know, was the loft option a bad idea for the MVHR unit, the ducting or both? I plan to have mine in the loft but the pipes will mainly be short runs in the loft then right into the thermal envelope. I might try making a little insulated room within the loft to house the unit and the manifolds and monitor the temperatures within as an experiment. I won't know the results of this until built and too late but hoping it might help.

This is the only small problem, I asked the person who sources the bricks at competitive rates for our local merchants for a certain amount of engineering bricks like staff blues from a brand that is close to the amount i require, so I'm not buying packs and having hundreds spare and they came back with the the above brick saying as long as they're S2 F2 they're all suitable. I think I need around 900. The light grey brick I chose for the house is F2 S2 and 10% but I can tell it would be crap if used below DPC so I just wondered if theres more to it. A Staff blue you can tell just holding it.

Could someone advise on the best type of brick to use below DPC on a house. I need to select a black brick for 3 courses below DPC, 1 course will be under the side path level and the other two courses will be above finish ground level. Some searches say 4.5% and others say 7.5% water absorption. I was recommended the following brick which is 12% absorption, and is F2 S2. My facing bricks above DPC are <10% and F2 S2.

I didn't think RB would support the weight of 2 boards hanging from it. When RB is screwed to joists and then you screw the boards to it, is there any movement if you press the ceiling upwards or is everything as solid as board direct onto joists?

Your going to mount the resilient bars onto a double boarded ceiling then hang a third layer of board off the bars? Some people add green glue or a cheaper equivalent between double boards. Not sure how effective it is.

@joe90 Thanks Joe, 150mm is a decent amount too, I'd be disappoint to and wasn't going to put any more in. I'd be interested to know if doubling up the boards would make a lot of difference or if it's just expected to make an improvement, I've added much thicker boards in the past 25mm and wasn't overly impressed. Sound bars are supposed to really help, maybe even work out the same as double boards. Are your rooms above carpet & underlay or hard floor?

I've seen a few comments on old posts mentioning doubling up the plasterboards. I wasn't sure if it's worth it for the cost vs difference it would make. I've used 15mm sound block before and in an old house lined a floor & neighbouring wall with 25mm plank which is just a 25mm thick x 600 x 3000mm plasterboard. I didn't find it too effective. I've just contacted Knauf about their products this afternoon, they seem much more reasonably priced for the loft & possibly floor void too. Was the iso roll for the stud walls and intermediate floor? I've never added slab or iso roll to an intermediate floor from the ground floor, I was lucky enough to drop it in from above and then lay my floor years ago. Is it hard to keep it in place until the plasterboard ceiling goes up? I have a 250mm posi joist void but have heating pipes to run, and then in the kitchen will have down lights sticking up into that space so it's where to position the 100 or 150mm insulation. Top, middle or lower part. 600mm centres.

Hi Joe, a bit of an old post, but out of interest, what did you add between your floors to be disappointed with the results? I have a similar post looking at decent ways to reduce sound between floors and stud walls without going over the top.

I'd be interested to know how good the drop seals work and with a good self closer and a threshold door seal that the door closes up to, can a decent seal be made around the whole perimeter? I don't have a drop seal but haven't been very successful in getting a good seal with a standard fire door between my utility room and garage. Maybe a good frame, seal and decent joiner would do better.

So the extra cost of increasing a sound slab from 25mm to 50mm or 50mm to 75mm thick is very minimal in terms of sound absorption? I understand that sound reduction is bit of a minefield and you can double up on plasterboard, use 15mm soundboard, resilient bars on ceilings etc. but it can get out of hand cost wise for a full build. What I don't want is to be able to hear every noise in a room above or below or through a wall and regret not doing that little bit more but I also don't want to spend £1000's more for very little gain. Areas for the best sound reduction I need are, one bedroom above a main living room and the main bathroom which is between two bedrooms and above a kitchen diner. Also the ground floor bathroom. In my current 1960's house with nothing between the floor, if you have a pish in the upstairs bathroom you can hear it in the kitchen like thunder 😀

Certainly isn't cheap at all. Temps is a better price but still expensive. Anything fire rated = double the price.

I'm pricing up various internal insulation for a self build and wondering if there's any good cheaper alternatives than the Rockwool brand for use stud walls and intermediate floor to reduce sound or is it the best? Also any good brands of mineral wool for a cold loft floor/upstairs ceiling. Stud walls specified - 75mm Rockwool RWA 45 - 45kg/m3 Intermediate floor specified - 100mm Rockwool flexi - 33Kg/m3 Loft - 400mm no brand specified. The Rockwool flexi seems to be a lot more expensive than RWA45 and the RWA45 is denser so surely better for sound absorption?

Just reading some old posts to gain some info. before I make a post of my own. I agree with what you say about the lower heat loss the lower the flow temperature can be. But why do people always say with low temperature systems to go for as close spacing as possible so you can get the heat into the room with it being at reduced flow temperature. I've completed all heat loss calcs for a self build and know that I'll be aiming for 37.5C MWT on weather compensation so this will vary the flow. Indoor designed to 21°C at outdoor -3.6°C. I will probably have the house running at 19°C air temperature but if designed higher it allows some headroom. I'm not sure if I go with 100mm centres throughout the ground floor 50mm screed or I have different spacings for the different heat loss rooms.

I'm all for simplicity at this stage, not yet broke ground but too far to make any big changes. Building regs are passed we are just swapping over from slab to B&B on the plans for a spring start I hope. No one seems overly concerned about adding or taking away a course in height as long as it's all vented correctly & following the standard construction. When you refer to a course of aerated block, do you mean like this image attached, or one of the below DPC courses?

I was just focusing on the block selection rather than the correct detail for floor insulation. I understand that but haven't worked with foundation blocks before. All the ones online seem to have strange sizes. I was hoping to just find some foundation blocks 440mm long x 215mm high in varying widths to suit my walls, 350mm, 300mm & whatever will go under the walls supporting 100mm beam ends that will only have single load bearing walls built above them. Most foundation blocks seem to be 3.6Kn not 7.2Kn and made from aerated material. Are these ok to use or problematic like the aerated blocks used above DPC which always have cracking issues? One of the builder I was looking to use still use the double dense block with infill method. Other than time, are there any cons to using this method nowadays? I just had a quick look, jablite 70 at 240mm would probably save me £700, the 160mm PIR was going to cost £1800. I''d need to raise the internal garage floor up by 75mm though to keep the heights correct between the house and garage step down. Jablite customer service staff were the least educated of any company I've ever dealt with in my life. Two women taking calls who said they have no training and no data at all on their own product.

Would the telescopic vents install ok as per sketch where the T beams & slip bricks are set on a course of brick?